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9L0-403 Mac OS X advocate Essentials 10.6

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9L0-403 exam Dumps Source : Mac OS X advocate Essentials 10.6

Test Code : 9L0-403
Test designation : Mac OS X advocate Essentials 10.6
Vendor designation : Apple
: 71 real Questions

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Apple Mac OS X Support

As Apple Macintosh turns 35, Android, Linux, OS X users obtain to rush its traditional apps | killexams.com real Questions and Pass4sure dumps

“Mac hacker Josh Juran has built an emulator, dubbed advanced Mac supersede (AMS), which promises to rush ancient Mac apps compiled for Motorola 68000-series CPUs on concomitant hardware,” Liam Tung reviews for ZDNet.

“With Apple’s Macintosh these days marking the thirty fifth anniversary of its launch, the undertaking may present fans of Mac apps from 1984 a random to relive the journey on Linux, Mac OS X, and Android instruments,” Tung reviews. “one of the key dreams of the AMS assignment, spotted by using Ars Technica, is to rush the apps with out wanting a replica of historical MacOS installing CDs as is needed for other Mac OS emulators.”

Tung studies, “Juran describes AMS as an ‘API-stage reimplementation of classic Mac OS’. The most efficient hardware AMS emulates is the 68000 CPU, and it’s built to labor without an Apple ROM or system application… AMS is soundless very plenty a piece in progress and presently only works on Mac OS X up to edition 10.2 on versions for both Intel and PowerPC CPUs. It won’t labor on MacOS Mojave. also, the Linux port doesn’t assist keyboard enter.”

read greater in the full article privilege here.

MacDailyNews Take: Juran’s “superior Mac replace” is privilege here.

If, like most of us, you’re working a macOS edition later than 10.2, which you could relive some historic-timey Mac goodness to your browser by pass of James friend’s PCE.js Mac Plus emulator operating Mac OS rig 7 privilege here.

[Thanks to MacDailyNews Reader “Fred Mertz” for the heads up.]


Are there are any VPN purchasers for Mac OS X that aid L2TP? | killexams.com real Questions and Pass4sure dumps

Our VPN is in accordance with determine point, using L2TP. Most americans privilege here exercise home windows, but i exercise Mac OS X 10.2.8 (Jaguar). Are there are any VPN consumers for Mac OS X that abet L2TP?

according to your query, I coincide with you might exist attempting to find a VPN client that runs L2TP over IPsec, the far off entry respond promoted via Microsoft, starting with home windows 2000. Many VPN gateway carriers (including assess element) in the beginning applied "vanilla" IPsec (tunnel mode) for host-to-community VPNs, however gain given that introduced L2TP over IPsec (transport mode) for interoperation with the embedded home windows VPN customer. this is top notch for home windows clients but, as you've got found, will besides exist a problem for others.

investigate point sells a version of their VPN-1 client for Mac OS eight.x/9.x, using vanilla IPsec. Apple's Mac OS X 10.3 (Panther) now comprises an embedded VPN customer that helps L2TP over IPsec. you're stuck in between with Mac OS 10.2.eight (Jaguar). Jaguar included embedded VPN code but not a graphical consumer interface to IPsec. Panther expands the Mac's embedded VPN customer, adding a graphical consumer interface to L2TP/IPsec, and is in reality your top-rated choice.

in case you can't upgrade to Panther, you may additionally are looking to are trying a 3rd-birthday celebration L2TP VPN customer for Jaguar. assess element-appropriate VPN shoppers for Mac OS 10.2 listed at Apple's internet website encompass Lobotomo IPsecuritas and Equinux VPN Tracker, despite the fact I can not construe from a brief examine product documentation no matter if these clients advocate L2TP/IPsec or just IPsec. that you can additionally try your hand at configuring Jaguar's embedded IPsec code the exercise of the command line interface. To learn more about configuring Jaguar's IPsec, perceive this PPT presentation via Paul Hoffman of the VPN Consortium. stand in intuition that you'd soundless need to configure L2TP on excellent of IPsec to pair along with your VPN gateway's coverage.


Apple issues macOS 10.14.three Supplemental update | killexams.com real Questions and Pass4sure dumps

Apple on Thursday up to date macOS Mojave with the unlock of the macOS 10.14.three Supplemental replace. The supersede became launched together with the iOS 12.1.four replace.

The Supplemental update fixes the group FaceTime trojan horse that has been making headlines recently. whereas most americans associate the bug with the iPhone, neighborhood FaceTime assist is attainable on macOS Mojave. The supersede additionally fixes a safety problem involving reside photographs in FaceTime. The safety notes for the Supplemental supersede can exist organize online.

earlier than installation any gadget update, duty a backup of your records. listed below are the steps for the setting up.

1. in the Finder, click on the Apple menu and search for an update indication for device Preferences, as shown within the image below. in case you perceive a demonstration for an replace, select rig Preferences.

sytem preference update mojaveIDG

If no longer, select About This Mac > Overview > utility replace.

2. you should definitely exist at the window for software update. Your Mac will check online to peer if the supersede is attainable. if it is, click on the supersede Now button.

three. A warning will seem, pointing out that your Mac will should restart. click on down load & Restart in case you can proceed. The down load will consume a few minutes and your Mac will instantly restart.

in case your Mac doesn’t restart, Go returned to the application supersede window and click on the update Now button. A Restart button may besides seem. click it to proceed.

To feel upon this article and different Macworld content material, visit their facebook page or their Twitter feed.

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Mac OS X advocate Essentials 10.6

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Mac OS X 10.6 Snow Leopard: the Ars Technica review | killexams.com real questions and Pass4sure dumps

Mac OS X 10.6 Snow Leopard: the Ars Technica review reader comments 454 with 269 posters participating, including epic author Share this story
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  • Mac OS X 10.4 Tiger: 150+  recent featuresMac OS X 10.4 Tiger: 150+ recent features

    In June of 2004, during the WWDC keynote address, Steve Jobs revealed Mac OS X 10.4 Tiger to developers and the public for the first time. When the finished product arrived in April of 2005, Tiger was the biggest, most important, most feature-packed release in the history of Mac OS X by a wide margin. Apple's marketing campaign reflected this, touting "over 150 recent features."

    All those recent features took time. Since its introduction in 2001, there had been at least one major release of Mac OS X each year. Tiger took over a year and a half to arrive. At the time, it definitely seemed worth the wait. Tiger was a hit with users and developers. Apple took the lesson to heart and quickly set expectations for the next major release of Mac OS X, Leopard. Through various channels, Apple communicated its remonstrate to coast from a 12-month to an 18-month release cycle for Mac OS X. Leopard was officially scheduled for "spring 2007."

    As the date approached, Apple's marketing machine trod a predictable path.

    Steve Jobs at WWDC 2007, touting 300  recent features in Mac OS X 10.5 LeopardSteve Jobs at WWDC 2007, touting 300 recent features in Mac OS X 10.5 Leopard

    Apple even went so far as to list whole 300 recent features on its website. As it turns out, "spring" was a bit optimistic. Leopard actually shipped at the immediate of October 2007, nearly two and a half years after Tiger. Did Leopard really gain twice as many recent features as Tiger? That's debatable. What's certain is that Leopard included a solid crop of recent features and technologies, many of which they now consume for granted. (For example, gain you had a discussion with a potential Mac user since the release of Leopard without mentioning Time Machine? I certainly haven't.)

    Mac OS X appeared to exist maturing. The progression was clear: longer release cycles, more features. What would Mac OS X 10.6 exist like? Would it arrive three and a half years after Leopard? Would it and involve 500 recent features? A thousand?

    At WWDC 2009, Bertrand Serlet announced a coast that he described as "unprecedented" in the PC industry.

    Mac OS X 10.6 - Read Bertrand's lips: No  recent Features!Mac OS X 10.6 - Read Bertrand's lips: No recent Features!

    That's right, the next major release of Mac OS X would gain no recent features. The product designation reflected this: "Snow Leopard." Mac OS X 10.6 would merely exist a variant of Leopard. Better, faster, more refined, more... uh... snowy.

    This was a risky strategy for Apple. After the rapid-fire updates of 10.1, 10.2, and 10.3 followed by the riot of recent features and APIs in 10.4 and 10.5, could Apple really obtain away with calling a "time out?" I imagine Bertrand was really sweating this announcement up on the stage at WWDC in front of a live audience of Mac developers. Their reaction? instinctive applause. There were even a few hoots and whistles.

    Many of these identical developers applauded the "150+ recent features" in Tiger and the "300 recent features" in Leopard at past WWDCs. Now they were applauding zero recent features for Snow Leopard? What explains this?

    It probably helps to know that the "0 recent Features" slide came at the immediate of an hour-long presentation detailing the major recent APIs and technologies in Snow Leopard. It was besides quickly followed by a back-pedaling ("well, there is one recent feature...") slide describing the addition of Microsoft Exchange support. In isolation, "no recent features" may seem to imply stagnation. In context, however, it served as a developer-friendly affirmation.

    The overall message from Apple to developers was something like this: "We're adding a ton of recent things to Mac OS X that will abet you write better applications and construct your existing code rush faster, and we're going to construct certain that whole this recent stuff is rock-solid and as bug-free as possible. We're not going to overextend ourselves adding a raft of recent customer-facing, marketing-friendly features. Instead, we're going to concentrate 100% on the things that move you, the developers."

    But if Snow Leopard is a savor note to developers, is it a Dear John note to users? You know, those people that the marketing department might so crudely refer to as "customers." What's in it for them? Believe it or not, the sales pitch to users is actually quite similar. As exhausting as it has been for developers to preserve up with Apple's seemingly never-ending stream of recent APIs, it can exist just as taxing for customers to abide on top of Mac OS X's features. Exposé, a recent Finder, Spotlight, a recent Dock, Time Machine, a recent Finder again, a recent iLife and iWork almost every year, and on and on. And as much as developers Hate bugs in Apple's APIs, users who undergo those bugs as application crashes gain just as much intuition to exist annoyed.

    Enter Snow Leopard: the release where they whole obtain a crash from the new-features/new-bugs treadmill of Mac OS X development. That's the pitch.

    Uncomfortable realities

    But wait a second, didn't I just mention an "hour-long presentation" about Snow Leopard featuring "major recent APIs and technologies?" When speaking to developers, Apple's message of "no recent features" is another pass of proverb "no recent bugs." Snow Leopard is suppositious to fix ancient bugs without introducing recent ones. But nothing says "new bugs, coming privilege up" quite like major recent APIs. So which is it?

    Similarly, for users, "no recent features" connotes stability and reliability. But if Snow Leopard includes enough changes to the core OS to fill an hour-long overview session at WWDC more than a year before its release, can Apple really construct superior on this promise? Or will users immediate up with whole the disadvantages of a feature-packed release like Tiger or Leopard—the inevitable 10.x.0 bugs, the unfamiliar, untried recent functionality—but without any of the actual recent features?

    Yes, it's enough to construct one quite cynical about Apple's real motivations. To toss some more fuel on the fire, gain a stare at the Mac OS X release timeline below. Next to each release, I've included a list of its most significant features.

    Mac OS X release timelineMac OS X release timeline

    That curve is taking on a decidedly droopy shape, as if it's being weighed down by the ever-increasing number of recent features. (The releases are distributed uniformly on the Y axis.) Maybe you reason it's reasonable for the time between releases to stretch out as each one brings a heavier load of goodies than the last, but preserve in intuition the rational consequence of such a curve over the longhorn haul.

    And yeah, there's a slight upwards kick at the immediate for 10.6, but remember, this is suppositious to exist the "no recent features" release. Version 10.1 had a similar no-frills focus but took a heck of a lot less time to arrive.

    Looking at this graph, it's hard not to marvel if there's something siphoning resources from the Mac OS X evolution effort. Maybe, say, some project that's in the first two or three major releases of its life, soundless in that steep, early section of its own timeline graph. Yes, I'm talking about the iPhone, specifically iPhone OS. The iPhone trade has exploded onto Apple's equipoise sheets like no other product before, even the iPod. It's besides accruing developers at an alarming rate.

    It's not a stretch to imagine that many of the artists and developers who piled on the user-visible features in Mac OS X 10.4 and 10.5 gain been reassigned to iPhone OS (temporarily or otherwise). After all, Mac OS X and iPhone OS share the identical core operating system, the identical language for GUI development, and many of the identical APIs. Some workforce migration seems inevitable.

    And let's not forget the "Mac OS X" technologies that they later erudite were developed for the iPhone and just happened to exist announced for the Mac first (because the iPhone was soundless a secret), like Core Animation and code signing. Such plot theories certainly aren't helped by WWDC keynote snubs and other indignities suffered by Mac OS X and the Mac in general since the iPhone arrived on the scene. And so, on top of everything else, Snow Leopard is tasked with restoring some luster to Mac OS X.

    Got whole that? A nearly two-year evolution cycle, but no recent features. Major recent frameworks for developers, but few recent bugs. Significant changes to the core OS, but more reliability. And a franchise rejuvenation with few user-visible changes.

    It's enough to circle a leopard white.

    The charge of entry

    Snow Leopard's opening overture to consumers is its price: $29 for those upgrading from Leopard. The debut release of Mac OS X 10.0 and the ultimate four major releases gain whole been $129, with no special pricing for upgrades. After eight years of this kindly of fiscal disciplining, Leopard users may well exist tempted to desist reading privilege now and just Go pick up a copy. Snow Leopard's upgrade charge is well under the impulse purchase threshold for many people. Twenty-nine dollars plus some minimal flat of faith in Apple's faculty to better the OS with each release, and boom, instant purchase.

    Still here? Good, because there's something else you need to know about Snow Leopard. It's an overture of a different sort, less of a come-on and more of a spur. Snow Leopard will only rush on Macs with Intel CPUs. Sorry (again), PowerPC fans, but this is the immediate of the line for you. The transition to Intel was announced over four years ago, and the ultimate recent PowerPC Mac was released in October 2005. It's time.

    But if Snow Leopard is meant to prod the PowerPC holdouts into the Intel age, its "no recent features" stance (and the accompanying lack of added visual flair) is working against it. For those running Leopard on a PowerPC-based Mac, there's precious slight in Snow Leopard to abet propel them over the (likely) four-digit charge wall of a recent Mac. For PowerPC Mac owners, the threshold for a recent Mac purchase remains mostly unchanged. When their ancient Mac breaks or seems too slow, they'll Go out and buy a recent one, and it'll approach with Snow Leopard pre-installed.

    If Snow Leopard does immediate up motivating recent Mac purchases by PowerPC owners, it will probably exist the result of resignation rather than inspiration. An Intel-only Snow Leopard is most significant for what it isn't: a further extension of PowerPC life advocate on the Mac platform.

    The final intriguing group is owners of Intel-based Macs that are soundless running Mac OS X 10.4 Tiger. Apple shipped Intel Macs with Tiger installed for a slight over one year and nine months. Owners of these machines who never upgraded to Leopard are not eligible for the $29 upgrade to Snow Leopard. They're besides apparently not eligible to purchase Snow Leopard for the traditional $129 price. Here's what Apple has to Tell about Snow Leopard's pricing (emphasis added).

    Mac OS X version 10.6 Snow Leopard will exist available as an upgrade to Mac OS X version 10.5 Leopard in September 2009 [...] The Snow Leopard separate user license will exist available for a suggested retail charge of $29 (US) and the Snow Leopard Family Pack, a separate household, five-user license, will exist available for a suggested charge of $49 (US). For Tiger® users with an Intel-based Mac, the Mac Box Set includes Mac OS X Snow Leopard, iLife® '09 and iWork® '09 and will exist available for a suggested charge of $169 (US) and a Family Pack is available for a suggested charge of $229 (US).

    Ignoring the family packs for a moment, this means that Snow Leopard will either exist free with your recent Mac, $29 if you're already running Leopard, or $169 if you gain an Intel Mac running Tiger. People upgrading from Tiger will obtain the latest version of iLife and iWork in the shrink (if that's the usurp term), whether they want them or not. It certain seems like there's an obvious status in this lineup for a $129 offering of Snow Leopard on its own. Then again, perhaps it whole comes down to how, exactly, Apple enforces the $29 Snow Leopard upgrade policy.

    (As an aside to non-Mac users, note that the non-server version of Mac OS X has no per-user serial number and no activation scheme of any kind, and never has. "Registration" with Apple during the Mac OS X install process is entirely optional and is only used to collect demographic information. Failing to register (or entering entirely bogus registration information) has no effect on your faculty to rush the OS. This is considered a genuine handicap of Mac OS X, but it besides means that Apple has no trustworthy record of who, exactly, is a "legitimate" owner of Leopard.)

    One possibility was that the $29 Snow Leopard upgrade DVD would only install on top of an existing installation of Leopard. Apple has done this character of thing before, and it bypasses any proof-of-purchase annoyances. It would, however, insert a recent problem. In the event of a hard drive failure or simple determination to reinstall from scratch, owners of the $29 Snow Leopard upgrade would exist forced to first install Leopard and then install Snow Leopard on top of it, perhaps more than doubling the installation time—and quintupling the annoyance.

    Given Apple's history in this area, no one should gain been surprised to find out that Apple chose the much simpler option: the $29 "upgrade" DVD of Snow Leopard will, in fact, install on any supported Mac, whether or not it has Leopard installed. It will even install onto an entirely blank hard drive.

    To exist clear, installing the $29 upgrade to Snow Leopard on a system not already running a properly licensed copy of Leopard is a violation of the end-user license agreement that comes with the product. But Apple's determination is a refreshing change: rewarding honest people with a hassle-free product rather than trying to discipline dishonest people by treating everyone like a criminal. This "honor system" upgrade enforcement policy partially explains the mountainous jump to $169 for the Mac Box Set, which ends up re-framed as an honest person's pass to obtain iLife and iWork at their accustomed prices, plus Snow Leopard for $11 more.

    And yes, speaking of installing, let's finally obtain on with it.

    Installation

    Apple claims that Snow Leopard's installation process is "up to 45% faster." Installation times vary wildly depending on the speed, contents, and fragmentation of the target disk, the speed of the optical drive, and so on. Installation besides only happens once, and it's not really an intriguing process unless something goes terribly wrong. Still, if Apple's going to construct such a claim, it's worth checking out.

    To eradicate as many variables as possible, I installed both Leopard and Snow Leopard from one hard disk onto another (empty) one. It should exist illustrious that this change negates some of Snow Leopard's most necessary installation optimizations, which are focused on reducing random data access from the optical disc.

    Even with this disadvantage, the Snow Leopard installation took about 20% less time than the Leopard installation. That's well short of Apple's "up to 45%" claim, but perceive above (and don't forget the "up to" weasel words). Both versions installed in less than 30 minutes.

    What is striking about Snow Leopard's installation is how quickly the initial Spotlight indexing process completed. Here, Snow Leopard was 74% faster in my testing. Again, the times are wee (5:49 vs. 3:20) and again, recent installations on blank disks are not the norm. But the shorter wait for Spotlight indexing is worth noting because it's the first indication most users will obtain that Snow Leopard means trade when it comes to performance.

    Another notable thing about installation is what's not installed by default: Rosetta, the facility that allows PowerPC binaries to rush on Intel Macs. Okay Apple, they obtain it. PowerPC is a stiff, bereft of life. It rests in peace. It's rung down the curtain and joined the choir invisible. As far as Apple is concerned, PowerPC is an ex-ISA.

    But not installing Rosetta by default? That seems a slight harsh, even foolhardy. What's going to befall when whole those users upgrade to Snow Leopard and then double-click what they've probably long since forgotten is a PowerPC application? Perhaps surprisingly, this is what happens:

    Rosetta: auto-installed for your convenienceRosetta: auto-installed for your convenience

    That's what I saw when I tried to launch Disk Inventory X on Snow Leopard, an application that, yes, I had long since forgotten was PowerPC-only. After I clicked the "Install" button, I actually expected to exist prompted to insert the installer DVD. Instead, Snow Leopard reached out over the network, pulled down Rosetta from an Apple server, and installed it.

    Rosetta auto-install

    No reboot was required, and Disk Inventory X launched successfully after the Rosetta installation completed. Mac OS X has not historically made much exercise of the install-on-demand approach to system software components, but the facility used to install Rosetta appears quite robust. Upon clicking "Install," an XML property list containing a vast catalog of available Mac OS X packages was downloaded. Snow Leopard uses the identical facility to download and install printer drivers on demand, saving another trip to the installer DVD. I hope this technique gains even wider exercise in the future.

    Installation footprint

    Rosetta aside, Snow Leopard simply puts fewer bits on your disk. Apple claims it "takes up less than half the disk space of the previous version," and that's no lie. A clean, default install (including fully-generated Spotlight indexes) is 16.8 GB for Leopard and 5.9 GB for Snow Leopard. (Incidentally, these numbers are both powers-of-two measurements; perceive sidebar.)

    A gigabyte by any other name

    Snow Leopard has another trick up its sleeve when it comes to disk usage. The Snow Leopard Finder considers 1 GB to exist equal to 109 (1,000,000,000) bytes, whereas the Leopard Finder—and, it should exist noted, every version of the Finder before it—equates 1 GB to 230 (1,073,741,824) bytes. This has the effect of making your hard disk suddenly exhibit larger after installing Snow Leopard. For example, my "1 TB" hard drive shows up in the Leopard Finder as having a capacity of 931.19 GB. In Snow Leopard, it's 999.86 GB. As you might gain guessed, hard disk manufacturers exercise the powers-of-ten system. It's whole quite a mess, really. Though I approach down pretty firmly on the powers-of-two side of the fence, I can't blame Apple too much for wanting to match up nicely with the long-established (but soundless dumb, intuition you) hard disk vendors' capacity measurement standard.

    Snow Leopard has several weight loss secrets. The first is obvious: no PowerPC advocate means no PowerPC code in executables. Recall the maximum feasible binary payload in a Leopard executable: 32-bit PowerPC, 64-bit PowerPC, x86, and x86_64. Now cross half of those architectures off the list. Granted, very few applications in Leopard included 64-bit code of any kind, but it's a 50% reduction in size for executables no matter how you slice it.

    Of course, not whole the files in the operating system are executables. There are data files, images, audio files, even a slight video. But most of those non-executable files gain one thing in common: they're usually stored in compressed file formats. Images are PNGs or JPEGs, audio is AAC, video is MPEG-4, even preference files and other property lists now default to a compact binary format rather than XML.

    In Snow Leopard, other kinds of files climb on board the compression bandwagon. To give just one example, ninety-seven percent of the executable files in Snow Leopard are compressed. How compressed? Let's look:

    % cd Applications/Mail.app/Contents/MacOS % ls -l Mail -rwxr-xr-x@ 1 root wheel 0 Jun 18 19:35 Mail

    Boy, that's, uh, pretty small, huh? Is this really an executable or what? Let's check their assumptions.

    % file Applications/Mail.app/Contents/MacOS/Mail Applications/Mail.app/Contents/MacOS/Mail: empty

    Yikes! What's going on here? Well, what I didn't construe you is that the commands shown above were rush from a Leopard system looking at a Snow Leopard disk. In fact, whole compressed Snow Leopard files exhibit to contain zero bytes when viewed from a pre-Snow Leopard version of Mac OS X. (They stare and act perfectly middling when booted into Snow Leopard, of course.)

    So, where's the data? The slight "@" at the immediate of the permissions string in the ls output above (a feature introduced in Leopard) provides a clue. Though the Mail executable has a zero file size, it does gain some extended attributes:

    % xattr -l Applications/Mail.app/Contents/MacOS/Mail com.apple.ResourceFork: 0000 00 00 01 00 00 2C F5 F2 00 2C F4 F2 00 00 00 32 .....,...,.....2 0010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ (184,159 lines snipped) 2CF610 63 6D 70 66 00 00 00 0A 00 01 FF FF 00 00 00 00 cmpf............ 2CF620 00 00 00 00 .... com.apple.decmpfs: 0000 66 70 6D 63 04 00 00 00 A0 82 72 00 00 00 00 00 fpmc......r.....

    Ah, there's whole the data. But wait, it's in the resource fork? Weren't those deprecated about eight years ago? Indeed they were. What you're witnessing here is yet another addition to Apple's favorite file system hobbyhorse, HFS+.

    At the dawn of Mac OS X, Apple added journaling, symbolic links, and hard links. In Tiger, extended attributes and access control lists were incorporated. In Leopard, HFS+ gained advocate for hard links to directories. In Snow Leopard, HFS+ learns another recent trick: per-file compression.

    The presence of the com.apple.decmpfs ascribe is the first hint that this file is compressed. This ascribe is actually hidden from the xattr command when booted into Snow Leopard. But from a Leopard system, which has no information of its special significance, it shows up as unpretentious as day.

    Even more information is revealed with the abet of Mac OS X Internals guru Amit Singh's hfsdebug program, which has quietly been updated for Snow Leopard.

    % hfsdebug /Applications/Mail.app/Contents/MacOS/Mail ... compression magic = cmpf compression character = 4 (resource fork has compressed data) uncompressed size = 7500336 bytes

    And certain enough, as they saw, the resource fork does indeed contain the compressed data. Still, why the resource fork? It's whole portion of Apple's usual, clever backward-compatibility gymnastics. A recent instance is the pass that hard links to directories point to up—and function—as aliases when viewed from a pre-Leopard version of Mac OS X.

    In the case of a HFS+ compression, Apple was (understandably) unable to construct pre-Snow Leopard systems read and interpret the compressed data, which is stored in ways that did not exist at the time those earlier operating systems were written. But rather than letting applications (and users) running on pre-10.6 systems choke on—or worse, debase through modification—the unexpectedly compressed file contents, Apple has chosen to cloak the compressed data instead.

    And where can the complete contents of a potentially large file exist hidden in such a pass that pre-Snow Leopard systems can soundless copy that file without the loss of data? Why, in the resource fork, of course. The Finder has always correctly preserved Mac-specific metadata and both the resource and data forks when stirring or duplicating files. In Leopard, even the lowly cp and rsync commands will effect the same. So while it may exist a slight bit spooky to perceive whole those "empty" 0 KB files when looking at a Snow Leopard disk from a pre-Snow Leopard OS, the random of data loss is small, even if you coast or copy one of the files.

    The resource fork isn't the only status where Apple has decided to smuggle compressed data. For smaller files, hfsdebug shows the following:

    % hfsdebug /etc/asl.conf ... compression magic = cmpf compression character = 3 (xattr has compressed data) uncompressed size = 860 bytes

    Here, the data is wee enough to exist stored entirely within an extended attribute, albeit in compressed form. And then, the final frontier:

    % hfsdebug /Volumes/Snow Time/Applications/Mail.app/Contents/PkgInfo ... compression magic = cmpf compression character = 3 (xattr has inline data) uncompressed size = 8 bytes

    That's right, an entire file's contents stored uncompressed in an extended attribute. In the case of a criterion PkgInfo file like this one, those contents are the four-byte classic Mac OS character and creator codes.

    % xattr -l Applications/Mail.app/Contents/PkgInfo com.apple.decmpfs: 0000 66 70 6D 63 03 00 00 00 08 00 00 00 00 00 00 00 fpmc............ 0010 FF 41 50 50 4C 65 6D 61 6C .APPLemal

    There's soundless the identical "fpmc..." preamble seen in whole the earlier examples of the com.apple.decmpfs attribute, but at the immediate of the value, the expected data appears as unpretentious as day: character code "APPL" (application) and creator code "emal" (for the Mail application—cute, as per classic Mac OS tradition).

    You may exist wondering, if this is whole about data compression, how does storing eight uncompressed bytes plus a 17-byte preamble in an extended ascribe deliver any disk space? The respond to that lies in how HFS+ allocates disk space. When storing information in a data or resource fork, HFS+ allocates space in multiples of the file system's allocation block size (4 KB, by default). So those eight bytes will consume up a minimum of 4,096 bytes if stored in the traditional way. When allocating disk space for extended attributes, however, the allocation block size is not a factor; the data is packed in much more tightly. In the end, the actual space saved by storing those 25 bytes of data in an extended ascribe is over 4,000 bytes.

    But compression isn't just about saving disk space. It's besides a classic instance of trading CPU cycles for decreased I/O latency and bandwidth. Over the past few decades, CPU performance has gotten better (and computing resources more plentiful—more on that later) at a much faster rate than disk performance has increased. Modern hard disk quest times and rotational delays are soundless measured in milliseconds. In one millisecond, a 2 GHz CPU goes through two million cycles. And then, of course, there's soundless the actual data transfer time to consider.

    Granted, several levels of caching throughout the OS and hardware labor mightily to cloak these delays. But those bits gain to approach off the disk at some point to fill those caches. Compression means that fewer bits gain to exist transferred. Given the almost comical glut of CPU resources on a modern multi-core Mac under middling use, the total time needed to transfer a compressed payload from the disk and exercise the CPU to decompress its contents into recollection will soundless usually exist far less than the time it'd consume to transfer the data in uncompressed form.

    That explains the potential performance benefits of transferring less data, but the exercise of extended attributes to store file contents can actually construct things faster, as well. It whole has to effect with data locality.

    If there's one thing that slows down a hard disk more than transferring a large amount of data, it's stirring its heads from one portion of the disk to another. Every coast means time for the head to start moving, then stop, then ensure that it's correctly positioned over the desired location, then wait for the spinning disk to attach the desired bits beneath it. These are whole real, physical, stirring parts, and it's fabulous that they effect their dance as quickly and efficiently as they do, but physics has its limits. These motions are the real performance killers for rotational storage like hard disks.

    The HFS+ volume format stores whole its information about files—metadata—in two primary locations on disk: the Catalog File, which stores file dates, permissions, ownership, and a host of other things, and the Attributes File, which stores "named forks."

    Extended attributes in HFS+ are implemented as named forks in the Attributes File. But unlike resource forks, which can exist very large (up to the maximum file size supported by the file system), extended attributes in HFS+ are stored "inline" in the Attributes File. In practice, this means a restrict of about 128 bytes per attribute. But it besides means that the disk head doesn't need to consume a trip to another portion of the disk to obtain the actual data.

    As you can imagine, the disk blocks that construct up the Catalog and Attributes files are frequently accessed, and therefore more likely than most to exist in a cache somewhere. whole of this conspires to construct the complete storage of a file, including both its metadata in its data, within the B-tree-structured Catalog and Attributes files an overall performance win. Even an eight-byte payload that balloons to 25 bytes is not a concern, as long as it's soundless less than the allocation block size for middling data storage, and as long as it whole fits within a B-tree node in the Attributes File that the OS has to read in its entirety anyway.

    There are other significant contributions to Snow Leopard's reduced disk footprint (e.g., the removal of unnecessary localizations and "designable.nib" files) but HFS+ compression is by far the most technically interesting.

    Installer intelligence

    Apple makes two other intriguing promises about the installation process:

    Snow Leopard checks your applications to construct certain they're compatible and sets aside any programs known to exist incompatible. In case a power outage interrupts your installation, it can start again without losing any data.

    The setting aside of "known incompatible" applications is undoubtedly a response to the "blue screen" problems some users encountered when upgrading from Tiger to Leopard two years ago, which was caused by the presence of incompatible—and some would Tell "illicit"—third-party system extensions. I gain a decidedly pragmatic view of such software, and I'm glad to perceive Apple taking a similarly practical approach to minimizing its impact on users.

    Apple can't exist expected to detect and disable whole potentially incompatible software, of course. I suspect only the most approved or highest profile risky software is detected. If you're a developer, this installer feature may exist a superior pass to find out if you're on Apple's sh*t list.

    As for continuing an installation after a power failure, I didn't gain the guts to test this feature. (I besides gain a UPS.) For long-running processes like installation, this kindly of added robustness is welcome, especially on battery-powered devices like laptops.

    I mention these two details of the installation process mostly because they highlight the kinds of things that are feasible when developers at Apple are given time to polish their respective components of the OS. You might reason that the installer team would exist hard-pressed to approach up with enough to effect during a nearly two-year evolution cycle. That's clearly not the case, and customers will gleam the benefits.

    Snow Leopard's recent looks

    I've long yearned for Apple to construct a antiseptic break, at least visually, from Mac OS X's Aqua past. Alas, I will exist waiting a bit longer, because Snow Leopard ushers in no such revolution. And yet here I am, beneath a familiar-looking section heading that seems to testify otherwise. The verisimilitude is, Snow Leopard actually changes the appearance of nearly every pixel on your screen—but not in the pass you might imagine.

    Since the dawn of color on the Macintosh, the operating system has used a default output gamma correction value of 1.8. Meanwhile, Windows—aka the relaxation of the world—has used a value of 2.2. Though this may not seem significant to anyone but professional graphics artists, the incompatibility is usually unpretentious to even a casual observer when viewing the identical image on both kinds of displays side by side.

    Though Mac users will probably instinctively prefer the 1.8 gamma image that they're used to, Apple has decided that this historical incompatibility is more distress than it's worth. The default output gamma correction value in Snow Leopard is now 2.2, just like everyone else. Done and done.

    If they notice at all, users will likely undergo this change as a passion that the Snow Leopard user interface has a bit more contrast than Leopard's. This is reinforced by the recent default desktop background, a re-drawn, more saturated version of Leopard's default desktop. (Note that these are two entirely different images and not an attempt to demonstrate the effects of different gamma correction settings.)

    LeopardLeopard Snow LeopardSnow Leopard Dock Exposé spotlight effectDock Exposé spotlight effect

    But even beyond color correction, staunch to form, Apple could not resist adding a few graphical tweaks to the Snow Leopard interface. The most unpretentious changes are related to the Dock. First, there's the recent "spotlight" stare triggered by a click-and-hold on an application icon in the Dock. (This activates Exposé, but only for the windows belonging to the application that was clicked. More later.)

    Furthermore, any and whole pop-up menus on the Dock—and only on the Dock—have a unique stare in Snow Leopard, complete with a custom selection appearance (which, for a change, does a passable job of matching the system-wide selection appearance setting).

    New Dock menu appearance. Mmmm… arbitrary.New Dock menu appearance. Mmmm… arbitrary.

    For Mac users of a certain age, these menus may bring to intuition Apple's Hi-Tech appearance theme from the bad-old days of Copland. They're actually considerably more subtle, however. Note the translucent edges which accentuate the rounded corners. The gradient on the selection highlight is besides admirably restrained.

    Nevertheless, this is an entirely recent stare for a separate (albeit commonly used) application, and it does clash a bit with the default "slanty, shiny shelf" appearance of the Dock. But I've already had my Tell about that, and more. If the oath of Snow Leopard's appearance was to "first, effect no harm," then I reason I'm inclined to give it a passing grade—almost.

    If I had to characterize what's wrong with Snow Leopard's visual additions with just two words, it'd exist these: everything fades. Apple has sprinkled Core Animation fairy dust over seemingly every application in Snow Leopard. If any portion of the user interface appears, disappears, or changes in any significant way, it's accompanied by an animation and one or more fades.

    In moderation, such effects are fine. But in several instances, Snow Leopard crosses the line. Or rather, it crosses my line, which, it should exist noted, is located far inside the territories of Candy Land. Others with a much lower tolerance for animations who are already galled by the frippery in Leopard and earlier releases will find slight to savor in Snow Leopard's visual changes.

    The one that really drove me over the edge is the fussy slight dance of the filename locality that occurs in the Finder (surprise!) when renaming a file on the desktop. There's just something about so many cross-fades, color changes, and text offsets occurring so rapidly and concentrated into such a wee locality that makes me want to scream. And whether or not I'm actually waiting for these animations to finish before I can continue to exercise my computer, it certainly feels that pass sometimes.

    Still, I must unenthusiastically call that most middling people (i.e., the ones who will not read this entire article) will either find these added visual touches delightful, or (much more likely) not notice them at all.

    Branding

    Animation aside, the visual sameness of Snow Leopard presents a bit of a marketing challenge for Apple. Even beyond the obvious problem of how to promote an operating system upgrade with "no recent features" to consumers, there's the issue of how to obtain people to notice that this recent product exists at all.

    In the run-up to Snow Leopard's release, Apple stuck to a modified version of Leopard's outer space theme. It was in the keynote slideshows, on the WWDC banners, on the developer release DVDs, and whole over the Mac OS X section of Apple's website. The header image from Apple's Mac OS X webpage as of a week before Snow Leopard's release appears below. It's pretty nick and dried: outer space, stars, rich purple nebula, lens flare.

    Snow. The final frontier.Snow. The final frontier.

    Then came the golden master of Snow Leopard, which, in a pleasant change from past releases, was distributed to developers a few weeks before Snow Leopard hit the shelves. Its installer introduced an entirely different stare which, as it turns out, was carried over to the retail packaging. For a change, let's line up the discs instead of the packaging (which is rapidly shrinking to barely hem the disc anyway). Here's Mac OS X 10.0 through 10.6, top to bottom and left to right. (The 10.0 and 10.1 discs looked essentially identical and gain been coalesced.)

    One of these things is not like the others…One of these things is not like the others…

    Yep, it's a snow leopard. With actual snow on it. It's a bit on the nose for my taste, but it's not without its charms. And it does gain one mountainous thing going for it: it's immediately recognizable as something recent and different. "Unmistakable" is how I'd sum up the packaging. Eight years of the giant, centered, variously adorned "X" and then boom: a cat. There's slight random that anyone who's seen Leopard sitting on the shelf of their local Apple store for the past two years will fail to notice that this is a recent product.

    (If you'd like your own picture of Snowy the snow leopard (that's right, I've named him), Apple was kindly enough to involve a desktop background image with the OS. Self-loathing Windows users may download it directly.)

    Warning: internals ahead

    We've arrived at the start of the customary "internals" section. Snow Leopard is whole about internal changes, and this is reflected in the content of this review. If you're only interested in the user-visible changes, you can skip ahead, but you'll exist missing out on the meat of this review and the heart of Apple's recent OS.

    64-bit: the road leads ever on

    Mac OS X started its journey to 64-bit back in 2003 with the release of Panther, which included the bare minimum advocate for the then-new PowerPC G5 64-bit CPU. In 2005, Tiger brought with it the faculty to create staunch 64-bit processes—as long as they didn't link with any of the GUI libraries. Finally, Leopard in 2007 included advocate for 64-bit GUI applications. But again, there was a caveat: 64-bit advocate extended to Cocoa applications only. It was, effectively, the immediate of the road for Carbon.

    Despite Leopard's seemingly impressive 64-bit bona fides, there are a few more steps before Mac OS X can achieve complete 64-bit nirvana. The diagrams below illustrate.

    64-bit in Mac OS X 10.4 Tiger 64-bit in Mac OS X 10.5 Leopard 64-bit in Mac OS X 10.6 Snow Leopard Mac OS X 10.4 Tiger Mac OS X 10.5 Leopard Mac OS X 10.6 Snow Leopard

    As we'll see, whole that yellow in the Snow Leopard diagram represents its capability, not necessarily its default mode of operation.

    K64

    Snow Leopard is the first version of Mac OS X to ship with a 64-bit kernel ("K64" in Apple's parlance), but it's not enabled by default on most systems. The intuition for this this is simple. Recall that there's no "mixed mode" in Mac OS X. At runtime, a process is either 32-bit or 64-bit, and can only load other code—libraries, plug-ins, etc.—of the identical kind.

    An necessary class of plug-ins loaded by the kernel is device drivers. Were Snow Leopard to default to the 64-bit kernel, only 64-bit device drivers would load. And seeing as Snow Leopard is the first version of Mac OS X to involve a 64-bit kernel, there'd exist precious few of those on customers' systems on launch day.

    And so, by default, Snow Leopard boots with a 64-bit kernel only on Xserves from 2008 or later. I guess the assumption is that whole of the devices commonly attached to an Xserve will exist supported by 64-bit drivers supplied by Apple in Snow Leopard itself.

    Perhaps surprisingly, not whole Macs with 64-bit processors are even able to boot into the 64-bit kernel. Though this may change in subsequent point releases of Snow Leopard, the table below lists whole the Macs that are either capable of or default to booting K64. (To find the "Model name" of your Mac, select "About This Mac" from the Apple menu, then click the "More info…" button and read the "Model Identifier" line in the window that appears.)

    Product Model name K64 status Early 2008 Mac Pro MacPro3,1 Capable Early 2008 Xserve Xserve2,1 Default MacBook Pro 15"/17" MacBookPro4,1 Capable iMac iMac8,1 Capable UniBody MacBook Pro 15" MacBookPro5,1 Capable UniBody MacBook Pro 17" MacBookPro5,2 Capable Mac Pro MacPro4,1 Capable iMac iMac9,1 Capable Early 2009 Xserve Xserve3,1 Default

    For whole K64-capable Macs, boot while holding down "6" and "4" keys simultaneously to select the 64-bit kernel. For a more permanent solution, exercise the nvram command to add arch=x86_64 to your boot-args string, or edit the file /Library/Preferences/SystemConfiguration/com.apple.Boot.plist and add arch=x86_64 to the Kernel Flags string:

    ... <key>Kernel</key> <string>mach_kernel</string> <key>Kernel Flags</key> <string>arch=x86_64</string> ...

    To switch back to the 32-bit kernel, hold down the "3" and "2" keys during boot, or exercise one of the techniques above, replacing "x86_64" with "i386".

    We've already discussed why, at least initially, you probably won't want to boot into K64. But as Snow Leopard adoption ramps up and 64-bit updates of existing kernel extensions become available, why might you actually want to exercise the 64-bit kernel?

    The first intuition has to effect with RAM, and not in the pass you might think. Though Leopard uses a 32-bit kernel, Macs running Leopard can contain and exercise far more RAM than the 4 GB restrict the "32-bit" qualifier might seem to imply. But as RAM sizes increase, there's another concern: address space depletion—not for applications, but for the kernel itself.

    As a 32-bit process, the kernel itself is limited to a 32-bit (i.e., 4GB) address space. That may not seem like a problem; after all, should the kernel really need more than 4GB of recollection to effect its job? But bethink that portion of the kernel's job is to track and manage system memory. The kernel uses a 64-byte structure to track the status of each 4KB page of RAM used on the system.

    That's 64 bytes, not kilobytes. It hardly seems like a lot. But now consider a Mac in the not-too-distant future containing 96GB of RAM. (If this sounds ridiculous to you, reason of how ridiculous the 8GB of RAM in the Mac I'm typing on privilege now would gain sounded to you five years ago.) Tracking 96GB of RAM requires 1.5GB of kernel address space. Using more than a third of the kernel's address space just to track recollection is a pretty uncomfortable situation.

    A 64-bit kernel, on the other hand, has a virtually unlimited kernel address space (16 exabytes). K64 is an inevitable necessity, given the rapidly increasing size of system memory. Though you may not need it today on the desktop, it's already common for servers to gain double-digit gigabytes of RAM installed.

    The other thing K64 has going for it is speed. The x86 instruction set architecture has had a bit of a tortured history. When designing the x86-64 64-bit extension of the x86 architecture, AMD took the break to leave behind some of the ugliness of the past and involve more modern features: more registers, recent addressing modes, non-stack-based floating point capabilities, etc. K64 reaps these benefits. Apple makes the following claims about its performance:

  • 250% faster system muster entry point
  • 70% faster user/kernel recollection copy
  • Focused benchmarking would stand these out, I'm sure. But in daily use, you're unlikely to exist able to ascribe any particular performance boost to the kernel. reason of K64 as removing bottlenecks from the few (usually server-based) applications that actually effect exercise these aspects of the kernel heavily.

    If it makes you feel better to know that your kernel is operating more efficiently, and that, were you to actually gain 96GB of RAM installed, you would not risk starving the kernel of address space, and if you don't gain any 32-bit drivers that you absolutely need to use, then by whole means, boot into the 64-bit kernel.

    For everyone else, my recommendation is to exist glad that K64 will exist ready and waiting for you when you eventually effect need it—and gladden effect hearten whole the vendors that construct kernel extensions that you custody about to add K64 advocate as soon as possible.

    Finally, this is worth repeating: gladden preserve in intuition that you effect not need to rush the 64-bit kernel in order to rush 64-bit applications or install more than 4GB of RAM in your Mac. Applications rush just fine in 64-bit mode on top of the 32-bit kernel, and even in earlier versions of Mac OS X it's been feasible to install and consume handicap of much more than 4GB of RAM.

    64-bit applications

    While Leopard may gain brought with it advocate for 64-bit GUI applications, it actually included very few of them. In fact, by my count, only two 64-bit GUI applications shipped with Leopard: Xcode (an optional install) and Chess. And though Leopard made it feasible for third-party developers to bear 64-bit (albeit Leopard-only) GUI applications, very few have—sometimes due to hapless realities, but most often because there's been no superior intuition to effect so, abandoning users of Mac OS X 10.4 or earlier in the process.

    Apple is now pushing the 64-bit transition much harder. This starts with leading by example. Snow Leopard ships with four end-user GUI applications that are not 64-bit: iTunes, Grapher, Front Row, and DVD Player. Everything else is 64-bit. The Finder, the Dock, Mail, TextEdit, Safari, iChat, Address Book, Dashboard, abet Viewer, Installer, Terminal, Calculator—you designation it, it's 64-bit.

    The second mountainous carrot (or stick, depending on how you stare at it) is the continued lack of 32-bit advocate for recent APIs and technologies. Leopard started the trend, leaving deprecated APIs behind and only porting the recent ones to 64-bit. The improved Objective-C 2.0 runtime introduced in Leopard was besides 64-bit-only.

    Snow Leopard continues along similar lines. The Objective-C 2.1 runtime's non-fragile instance variables, exception model unified with C++, and faster vtable dispatch remain available only to 64-bit applications. But the most significant recent 64-bit-only API is QuickTime X—significant enough to exist addressed separately, so abide tuned.

    64-bits or bust

    All of this is Apple's not-so-subtle pass of telling developers that the time to coast to 64-bit is now, and that 64-bit should exist the default for whole recent applications, whether a developer thinks it's "needed" or not. In most cases, these recent APIs gain no intrinsic connection to 64-bit. Apple has simply chosen to exercise them as additional forms of persuasion.

    Despite whole of the above, I'd soundless muster Snow Leopard merely the penultimate step in Mac OS X's journey to exist 64-bit from top to bottom. I fully anticipate Mac OS X 10.7 to boot into the 64-bit kernel by default, to ship with 64-bit versions of whole applications, plug-ins, and kernel extensions, and to leave even more legacy and deprecated APIs to fade away in the land of 32-bit.

    QuickTime X

    Apple did something a bit odd in Leopard when it neglected to port the C-based QuickTime API to 64-bit. At the time, it didn't seem like such a mountainous deal. Mac OS X's transition to 64-bit had already spanned many years and several major versions. One could imagine that it just wasn't yet QuickTime's circle to Go 64-bit.

    As it turns out, my terse but pessimistic assessment of the situation at the time was accurate: QuickTime got the "Carbon treatment". like Carbon, the venerable QuickTime API that they know and savor will not exist making the transition to 64-bit—ever.

    To exist clear, QuickTime the technology and QuickTime the brand will most definitely exist coming to 64-bit. What's being left behind in 32-bit-only form is the C-based API introduced in 1991 and built upon for 18 years thereafter. Its replacement in the world of 64-bit in Snow Leopard is the aptly named QuickTime X.

    The "X" in QuickTime X, like the one in in Mac OS X, is pronounced "ten." This is but the first of many eerie parallels. like Mac OS X before it, QuickTime X:

  • aims to construct a antiseptic crash from its predecessor
  • is based on technology originally developed for another platform
  • includes transparent compatibility with its earlier incarnation
  • promises better performance and a more modern architecture
  • lacks many necessary features in its initial release
  • Maximum available Mac CPU speed (MHz)Maximum available Mac CPU speed (MHz)

    Let's consume these one at a time. First, why is a antiseptic crash needed? attach simply, QuickTime is old—really old. The horribly blocky, postage-stamp-size video displayed by its initial release in 1991 was considered a technological tour de force.

    At the time, the fastest Macintosh money could buy contained a 25 MHz CPU. The ridiculous chart to the privilege is meant to hammer home this point. Forward-thinking design can only obtain you so far. The shape of the world a technology is born into eventually, inevitably dictates its fate. This is especially staunch for long-lived APIs like QuickTime with a strong bent towards backward compatibility.

    As the first successful implementation of video on a personal computer, it's frankly fabulous that the QuickTime API has lasted as long as it has. But the world has moved on. Just as Mac OS organize itself mired in a ghetto of cooperative multitasking and unprotected memory, QuickTime limps into 2009 with antiquated notions of concurrency and subsystem layering baked into its design.

    When it came time to write the video-handling code for the iPhone, the latest version of QuickTime, QuickTime 7, simply wasn't up to the task. It had grown too bloated and inefficient during its life on the desktop, and it lacked superior advocate for the GPU-accelerated video playback necessary to wield modern video codecs on a handheld (even with a CPU sixteen times the clock speed of any available in a Mac when QuickTime 1.0 was released). And so, Apple created a tight, modern, GPU-friendly video playback engine that could fit comfortably within the RAM and CPU constraints of the iPhone.

    Hmm. An aging desktop video API in need of a replacement. A fresh, recent video library with superior performance even on (comparatively) anemic hardware. Apple connected the dots. But the trick is always in the transition. Happily, this is Apple's forte. QuickTime itself has already lived on three different CPU architectures and three entirely different operating systems.

    The switch to 64-bit is yet another (albeit less dramatic) inflection point, and Apple has chosen it to ticket the restrict between the ancient QuickTime 7 and the recent QuickTime X. It's done this in Snow Leopard by limiting whole exercise of QuickTime by 64-bit applications to the QTKit Objective-C framework.

    QTKit's recent world order

    QTKit is not new; it began its life in 2005 as a more native-feeling interface to QuickTime 7 for Cocoa applications. This extra layer of abstraction is the key to the QuickTime X transition. QTKit now hides within its object-oriented walls both QuickTime 7 and QuickTime X. Applications exercise QTKit as before, and behind the scenes QTKit will select whether to exercise QuickTime 7 or QuickTime X to fulfill each request.

    If QuickTime X is so much better, why doesn't QTKit exercise it for everything? The respond is that QuickTime X, like its Mac OS X namesake, has very limited capabilities in its initial release. While QuickTime X supports playback, capture, and exporting, it does not advocate general-purpose video editing. It besides supports only "modern" video formats—basically, anything that can exist played by an iPod, iPhone, or Apple TV. As for other video codecs, well, you can forget about handling them with plug-ins because QuickTime X doesn't advocate those either.

    For every one of the cases where QuickTime X is not up to the job, QuickTime 7 will fill in. Cutting, copying, and pasting portions of a video? QuickTime 7. Extracting individual tracks from a movie? QuickTime 7. Playing any movie not natively supported by an existing Apple handheld device? QuickTime 7. Augmenting QuickTime's codec advocate using a plug-in of any kind? You guessed it: QuickTime 7.

    But wait a second. If QTKit is the only pass for a 64-bit application to exercise QuickTime, and QTKit multiplexes between QuickTime 7 and QuickTime X behind the scenes, and QuickTime 7 is 32-bit-only, and Mac OS X does not advocate "mixed mode" processes that can execute both 32-bit and 64-bit code, then how the heck does a 64-bit process effect anything that requires the QuickTime 7 back-end?

    To find out, fire up the recent 64-bit QuickTime Player application (which will exist addressed separately later) and open a movie that requires QuickTime 7. Let's say, one that uses the Sorenson video codec. (Remember that? superior times.) certain enough, it plays just fine. But search for "QuickTime" in the Activity Monitor application and you'll perceive this:

    Pretty sneaky, sis: 32-bit QTKitServer processPretty sneaky, sis: 32-bit QTKitServer process

    And the respond is revealed. When a 64-bit application using QTKit requires the services of the 32-bit-only QuickTime 7 back-end, QTKit spawns a divide 32-bit QTKitServer process to effect the labor and communicate the results back to the originating 64-bit process. If you leave Activity Monitor open while using the recent QuickTime Player application, you can watch the QTKitServer processes approach and Go as needed. This is whole handled transparently by the QTKit framework; the application itself need not exist watchful of these machinations.

    Yes, it's going to exist a long, long time before QuickTime 7 disappears completely from Mac OS X (at least Apple was kindly enough not to muster it "QuickTime Classic"), but the path forward is clear. With each recent release of Mac OS X, anticipate the capabilities of QuickTime X to expand, and the number of things that soundless require QuickTime 7 to decrease. In Mac OS X 10.7, for example, I imagine that QuickTime X will gain advocate for plug-ins. And surely by Mac OS X 10.8, QuickTime X will gain complete video editing support. whole this will exist happening beneath the unifying facade of QTKit until, eventually, the QuickTime 7 back-end is no longer needed at all.

    Say what you mean

    In the meantime, perhaps surprisingly, many of the current limitations of QuickTime X actually highlight its unique advantages and inform the evolving QTKit API. Though there is no direct pass for a developer to request that QTKit exercise the QuickTime X back-end, there are several roundabout means to influence the decision. The key is the QTKit API, which relies heavily on the concept of intent.

    QuickTime versions 1 through 7 exercise a separate representation of whole media resources internally: a Movie object. This representation includes information about the individual tracks that construct up the movie, the sample tables for each track, and so on—all the information QuickTime needs to understand and exploit the media.

    This sounds stately until you realize that to effect anything with a media resource in QuickTime requires the construction of this comprehensive Movie object. consider playing an MP3 file with QuickTime, for example. QuickTime must create its internal Movie remonstrate representation of the MP3 file before it can commence playback. Unfortunately, the MP3 container format seldom contains comprehensive information about the structure of the audio. It's usually just a stream of packets. QuickTime must laboriously scan and parse the entire audio stream in order to complete the Movie object.

    QuickTime 7 and earlier versions construct this process less painful by doing the scanning and parsing incrementally in the background. You can perceive this in many QuickTime-based player applications in the form of a progress bar overlaid on the movie controller. The image below shows a 63MB MP3 podcast loading in the Leopard version of QuickTime Player. The shaded portion of the movie timeline slowly fills the dotted locality from left to right.

    QuickTime 7 doing more  labor than necessary

    QuickTime 7 doing more labor than necessary

    Though playback can commence almost immediately (provided you play from the beginning, that is) it's worthwhile to consume a step back and consider what's going on here. QuickTime is creating a Movie remonstrate suitable for any operation that QuickTime can perform: editing, track extraction or addition, exporting, you designation it. But what if whole I want to effect is play the file?

    The distress is, the QuickTime 7 API lacks a pass to express this kindly of intent. There is no pass to Tell to QuickTime 7, "Just open this file as quickly as feasible so that I can play it. Don't bother reading every separate byte of the file from the disk and parsing it to determine its structure just in case I select to edit or export the content. That is not my intent. Please, just open it for playback."

    The QTKit API in Snow Leopard provides exactly this capability. In fact, the only pass to exist eligible for the QuickTime X back-end at whole is to explicitly express your intent not to effect anything QuickTime X cannot handle. Furthermore, any attempt to effect an operation that lies outside your previously expressed intent will occasions QTKit to raise an exception.

    The intent mechanism is besides the pass that the recent features of QuickTime X are exposed, such as the faculty to asynchronously load large or distantly located (e.g., over a behind network link) movie files without blocking the UI running on the main thread of the application.

    Indeed, there are many reasons to effect what it takes to obtain on board the QuickTime X train. For the media formats it supports, QuickTime X is less taxing on the CPU during playback than QuickTime 7. (This is beyond the fact that QuickTime X does not consume time preparing its internal representation of the movie for editing and export when playback is whole that's desired.) QuickTime X besides supports GPU-accelerated playback of H.264, but, in this initial release, only on Macs equipped with an NVIDIA 9400M GPU (i.e., some 2009 iMacs and several models of MacBooks from 2008 and 2009). Finally, QuickTime X includes comprehensive ColorSync advocate for video, which is long overdue.

    The X factor

    This is just the start of a long journey for QuickTime X, and seemingly not a very auspicious one, at that. A QuickTime engine with no editing support? No plug-ins? It seems ridiculous to release it at all. But this has been Apple's pass in recent years: steady, deliberate progress. Apple aims to ship no features before their time.

    As anxious as developers may exist for a full-featured, 64-bit successor to the QuickTime 7 engine, Apple itself is sitting on top of one of the largest QuickTime-riddled (and Carbon-addled, to boot) code bases in the industry: Final nick Studio. Thus far, It remains stuck in 32-bit. To Tell that Apple is "highly motivated" to extend the capabilities of QuickTime X would exist an understatement.

    Nevertheless, don't anticipate Apple to rush forward foolishly. Duplicating the functionality of a continually developed, 18-year-old API will not befall overnight. It will consume years, and it will exist even longer before every necessary Mac OS X application is updated to exercise QTKit exclusively. Transitions. Gotta savor 'em.

    File system API unification

    Mac OS X has historically supported many different ways of referring to files on disk from within an application. Plain-old paths (e.g., /Users/john/Documents/myfile) are supported at the lowest levels of the operating system. They're simple, predictable, but perhaps not such a stately understanding to exercise as the only pass an application tracks files. consider what happens if an application opens a file based on a path string, then the user moves that file somewhere else while it's soundless being edited. When the application is instructed to deliver the file, if it only has the file path to labor with, it will immediate up creating a recent file in the ancient location, which is almost certainly not what the user wanted.

    Classic Mac OS had a more sophisticated internal representation of files that enabled it to track files independent of their actual locations on disk. This was done with the abet of the unique file ids supported by HFS/HFS+. The Mac OS X incarnation of this concept is the FSRef data type.

    Finally, in the modern age, URLs gain become the de facto representation for files that may exist located somewhere other than the local machine. URLs can besides refer to local files, but in that case they gain whole the identical disadvantages as file paths.

    This diversity of data types is reflected in Mac OS X's file system APIs. Some functions consume file path as arguments, some anticipate opaque references to files, and soundless others labor only with URLs. Programs that exercise these APIs often disburse a lot of their time converting file references from one representation to another.

    The situation is similar when it comes to getting information about files. There are a huge number of file system metadata retrieval functions at whole levels of the operating system, and no separate one of them is comprehensive. To obtain whole available information about a file on disk requires making several divide calls, each of which may anticipate a different character of file reference as an argument.

    Here's an instance Apple provided at WWDC. Opening a separate file in the Leopard version of the Preview image viewer application results in:

  • Four conversions of an FSRef to a file path
  • Ten conversions of a file path to an FSRef
  • Twenty-five calls to getattrlist()
  • Eight calls to stat()/lstat()
  • Four calls to open()/close()
  • In Snow Leopard, Apple has created a new, unified, comprehensive set of file system APIs built around a separate data type: URLs. But these are URL "objects"—namely, the opaque data types NSURL and CFURL, with a toll-free bridge between them—that gain been imbued with whole the desirable attributes of an FSRef.

    Apple settled on these data types because their opaque nature allowed this kindly of enhancement, and because there are so many existing APIs that exercise them. URLs are besides the most future-proof of whole the choices, with the scheme portion providing nearly unlimited flexibility for recent data types and access mechanisms. The recent file system APIs built around these opaque URL types advocate caching and metadata prefetching for a further performance boost.

    There's besides a recent on-disk representation called a Bookmark (not to exist confused with a browser bookmark) which is like a more network-savvy replacement for classic Mac OS aliases. Bookmarks are the most robust pass to create a reference to a file from within another file. It's besides feasible to attach arbitrary metadata to each Bookmark. For example, if an application wants to preserve a persistent list of "favorite" files plus some application-specific information about them, and it wants to exist resilient to any movement of these files behind its back, Bookmarks are the best tool for the job.

    I mention whole of this not because I anticipate file system APIs to exist whole that intriguing to people without my particular fascination with this portion of the operating system, but because, like Core Text before it, it's an indication of exactly how immature Mac OS X really is as a platform. Even after seven major releases, Mac OS X is soundless struggling to coast out from the shadow of its three ancestors: NeXTSTEP, classic Mac OS, and BSD Unix. Or perhaps it just goes to point to how ruthlessly Apple's core OS team is driven to supersede ancient and crusty APIs and data types with new, more modern versions.

    It will exist a long time before the benefits of these changes trickle down (or is it up?) to end-users in the form of Mac applications that are written or modified to exercise these recent APIs. Most well-written Mac applications already exhibit most of the desirable behavior. For example, the TextEdit application in Leopard will correctly detect when a file it's working on has moved.

    TextEdit: a  superior Mac OS X citizenTextEdit: a superior Mac OS X citizen

    Of course, the key modifier here is "well-written." Simplifying the file system APIs means that more developers will exist willing to expend the effort—now greatly reduced—to provide such user-friendly behaviors. The accompanying performance boost is just icing on the cake, and one more intuition that developers might select to alter their existing, working application to exercise these recent APIs.

    Doing more with more

    Moore's Law is widely cited in technology circles—and besides widely misunderstood. It's most often used as shorthand for "computers double in speed every year or so," but that's not what Gordon Moore wrote at all. His 1965 article in Electronics magazine touched on many topics in the semiconductor industry, but if it had to exist summed up in a separate "law", it would be, roughly, that the number of transistors that fit onto a square inch of silicon doubles every 12 months.

    Moore later revised that to two years, but the time age is not what people obtain wrong. The problem is confusing a doubling of transistor density with a doubling of "computer speed." (Even more problematic is declaring a "law" based on a separate paper from 1965, but we'll attach that aside for now. For a more thorough discussion of Moore's Law, gladden read this classic article by Jon Stokes.)

    For decades, each enlarge in transistor density was, in fact, accompanied by a comparable enlarge in computing speed thanks to ever-rising clock speeds and the dawn of superscalar execution. This worked great—existing code ran faster on each recent CPU—until the grim realities of power density attach an immediate to the fun.

    Moore's Law continues, at least for now, but their faculty to construct code rush faster with each recent enlarge in transistor density has slowed considerably. The free lunch is over. CPU clock speeds gain stagnated for years, many times actually going backwards. (The latest top-of-the-line 2009 Mac Pro contains a 2.93 GHz CPU, whereas the 2008 model could exist equipped with a 3.2 GHz CPU.) Adding execution units to a CPU has besides long since reached the point of diminishing returns, given the limits of instruction-level parallelism in common application code.

    And yet we've soundless got whole these recent transistors raining down on us, more every year. The challenge is to find recent ways to exercise them to actually construct computers faster.

    Thus far, the semiconductor industry's respond has been to give us more of what they already have. Where once a CPU contained a separate rational processing unit, now CPUs in even the lowliest desktop computers contain two processor cores, with high-end models sporting two chips with eight rational cores each. Granted, the cores themselves are besides getting faster, usually by doing more at the identical clock speed as their predecessors, but that's not happening at nearly the rate that the cores are multiplying.

    Unfortunately, generally speaking, a dual-core CPU will not rush your application twice as hasty as a single-core CPU. In fact, your application probably won't rush any faster at whole unless it was written to consume handicap of more than just a separate rational CPU. Presented with a glut of transistors, chipmakers gain turned around and provided more computing resources than programmers know what to effect with, transferring much of the responsibility for making computers faster to the software guys.

    We're with the operating system and we're here to help

    It's into this environment that Snow Leopard is born. If there's one responsibility (aside from security) that an operating system vendor should feel in the year 2009, it's finding a pass for applications—and the OS itself—to utilize the ever-growing wealth of computing resources at their disposal. If I had to pick separate technological "theme" for Snow Leopard, this would exist it: helping developers utilize whole this newfound silicon; helping them effect more with more.

    To that end, Snow Leopard includes two significant recent APIs backed by several smaller, but equally necessary infrastructure improvements. We'll start at the bottom with, believe it or not, the compiler.

    LLVM and Clang

    Apple made a strategic investment in the LLVM open source project several years ago. I covered the fundamentals of LLVM in my Leopard review. (If you're not up to speed, gladden ensnare up on the topic before continuing.) In it, I described how Leopard used LLVM to provide dramatically more efficient JIT-compiled software implementations of OpenGL functions. I ended with the following admonition:

    Don't exist misled by its humble exercise in Leopard; Apple has stately plans for LLVM. How grand? How about swapping out the guts of the gcc compiler Mac OS X uses now and replacing them with the LLVM equivalents? That project is well underway. Not ambitious enough? How about ditching gcc entirely, replacing it with a completely recent LLVM-based (but gcc-compatible) compiler system? That project is called Clang, and it's already yielded some impressive performance results.

    With the introduction of Snow Leopard, it's official: Clang and LLVM are the Apple compiler strategy going forward. LLVM even has a snazzy recent logo, a not-so-subtle homage to a well-known compiler design textbook:

    LLVM! Clang! Rawr!

    LLVM! Clang! Rawr!

    Apple now offers a total of four compilers for Mac OS X: GCC 4.0, GCC 4.2, LLVM-GCC 4.2 (the GCC 4.2 front-end combined with an LLVM back-end), and Clang, in order of increasing LLVM-ness. Here's a diagram:

    Mac OS X compilers

    Mac OS X compilers

    All of these compilers are binary-compatible on Mac OS X, which means you can, for example, build a library with one compiler and link it into an executable built with another. They're besides whole command-line and source-compatible—in theory, anyway. Clang does not yet advocate some of the more esoteric features of GCC. Clang besides only supports C, Objective-C, and a slight bit of C++ (Clang(uage), obtain it?) whereas GCC supports many more. Apple is committed to full C++ advocate for Clang, and hopes to labor out the remaining GCC incompatibilities during Snow Leopard's lifetime.

    Clang brings with it the two headline attributes you anticipate in a hot, recent compiler: shorter compile times and faster executables. In Apple's testing with its own applications such as iCal, Address Book, and Xcode itself, plus third-party applications like Adium and Growl, Clang compiles nearly three times faster than GCC 4.2. As for the speed of the finished product, the LLVM back-end, whether used in Clang or in LLVM-GCC, produces executables that are 5-25% faster than those generated by GCC 4.2.

    Clang is besides more developer-friendly than its GCC predecessors. I concede that this topic doesn't gain much to effect with taking handicap of multiple CPU cores and so on, but it's certain to exist the first thing that a developer actually notices when using Clang. Indulge me.

    For starters, Clang is embeddable, so Xcode can exercise the identical compiler infrastructure for interactive features within the IDE (symbol look-up, code completion, etc.) as it uses to compile the final executable. Clang besides creates and preserves more extensive metadata while compiling, resulting in much better mistake reporting. For example, when GCC tells you this:

    GCC  mistake message for an unknown type

    It's not exactly pellucid what the problem is, especially if you're recent to C programming. Yes, whole you hotshots already know what the problem is (especially if you saw this instance at WWDC), but I reason everyone can coincide that this error, generated by Clang, is a lot more helpful:

    Clang  mistake message for an unknown type

    Maybe a novice soundless wouldn't know what to do, but at least it's pellucid where the problem lies. Figuring out why the compiler doesn't know about NSString is a much more focused task than can exist derived from GCC's cryptic error.

    Even when the message is clear, the context may not be. consume this mistake from GCC:

    GCC  mistake message for  evil operands

    Sure, but there are four "+" operators on that separate line. Which one has the problematic operands? Thanks to its more extensive metadata, Clang can pinpoint the problem:

    Clang  mistake message for  evil operands

    Sometimes the mistake is perfectly clear, but it just seems a bit off, like this situation where jumping to the mistake as reported by GCC puts you on the line below where you actually want to add the missing semicolon:

    GCC  mistake message for missing semicolon

    The slight things count, you know? Clang goes that extra mile:

    Clang  mistake message for missing semicolon

    Believe it or not, stuff like this means a lot to developers. And then there are the not-so-little things that exist necessary even more, like the LLVM-powered static analyzer. The image below shows how the static analyzer displays its discovery of a feasible bug.

    OH HAI I  organize UR BUGOH HAI I organize UR BUG

    Aside from the whimsy of the slight arrows (which, admit it, are adorable), the actual bug it's highlighting is something that every programmer can imagine creating (say, through some hasty editing). The static analyzer has determined that there's at least one path through this set of nested conditionals that leaves the myName variable uninitialized, thus making the attempt to transmit the mutableCopy message in the final line potentially dangerous.

    I'm certain Apple is going hog-wild running the static analyzer on whole of its applications and the operating system itself. The prospect of an automated pass to learn bugs that may gain existed for years in the depths of a huge codebase is almost pornographic to developers—platform owners in particular. To the degree that Mac OS X 10.6.0 is more bug-free than the previous 10.x.0 releases, LLVM surely deserves some significant portion of the credit.

    Master of the house

    By committing to a Clang/LLVM-powered future, Apple has finally taken complete control of its evolution platform. The CodeWarrior undergo apparently convinced Apple that it's unwise to confidence on a third party for its platform's evolution tools. Though it's taken many years, I reason even the most diehard Metrowerks fan would gain to coincide that Xcode in Snow Leopard is now a pretty damn superior IDE.

    After years of struggling with the disconnect between the goals of the GCC project and its own compiler needs, Apple has finally nick the apron strings. OK, granted, GCC 4.2 is soundless the default compiler in Snow Leopard, but this is a transitional phase. Clang is the recommended compiler, and the focus of whole of Apple's future efforts.

    I know what you're thinking. This is swell and all, but how are these compilers helping developers better leverage the expanding swarm of transistors at their disposal? As you'll perceive in the following sections, LLVM's scaly, metallic head pops up in a few key places.

    Blocks

    In Snow Leopard, Apple has introduced a C language extension called "blocks." Blocks add closures and anonymous functions to C and the C-derived languages C++, Objective-C, and Objective C++.

    These features gain been available in dynamic programming languages such as Lisp, Smalltalk, Perl, Python, Ruby, and even the unassuming JavaScript for a long time (decades, in the case of Lisp—a fact gladly offered by its practitioners). While dynamic-language programmers consume closures and anonymous functions for granted, those who labor with more traditional, statically compiled languages such as C and its derivatives may find them quite exotic. As for non-programmers, they likely gain no interest in this topic at all. But I'm going to attempt an explanation nonetheless, as blocks form the foundation of some other intriguing technologies to exist discussed later.

    Perhaps the simplest pass to construe blocks is that they construct functions another form of data. C-derived languages already gain duty pointers, which can exist passed around like data, but these can only point to functions created at compile time. The only pass to influence the conduct of such a duty is by passing different arguments to the duty or by setting global variables which are then accessed from within the function. Both of these approaches gain mountainous disadvantages

    Passing arguments becomes cumbersome as their number and complexity grows. Also, it may exist that you gain limited control over the arguments that will exist passed to your function, as is often the case with callbacks. To compensate, you may gain to bundle up whole of your intriguing status into a context remonstrate of some kind. But when, how, and by whom that context data will exist disposed of can exist difficult to pin down. Often, a second callback is required for this. It's whole quite a pain.

    As for the exercise of global variables, in addition to being a well-known anti-pattern, it's besides not thread-safe. To construct it so requires locks or some other form of mutual exclusion to preclude multiple invocations of the identical duty from stepping on each other's toes. And if there's anything worse than navigating a sea of callback-based APIs, it's manually dealing with thread safety issues.

    Blocks bypass whole of these problems by allowing functional blobs of code—blocks—to exist defined at runtime. It's easiest to understand with an example. I'm going to start by using JavaScript, which has a bit friendlier syntax, but the concepts are the same.

    b = get_number_from_user(); multiplier = function(a) { return a * b };

    Here I've created a duty named multiplier that takes a separate argument, a, and multiplies it by a second value, b, that's provided by the user at runtime. If the user supplied the number 2, then a muster to multiplier(5) would return the value 10.

    b = get_number_from_user(); // assume it's 2 multiplier = function(a) { return a * b }; r = multiplier(5); // 5 * 2 = 10

    Here's the instance above done with blocks in C.

    b = get_number_from_user(); // assume it's 2 multiplier = ^ int (int a) { return a * b; }; r = multiplier(5); // 5 * 2 = 10

    By comparing the JavaScript code to the C version, I hope you can perceive how it works. In the C example, that slight caret ^ is the key to the syntax for blocks. It's kindly of ugly, but it's very C-like in that it parallels the existing C syntax for duty pointers, with ^ in status of *, as this instance illustrates:

    /* A duty that takes a separate integer argument and returns a pointer to a duty that takes two integer arguments and returns a floating-point number. */ float (*func2(int a))(int, int); /* A duty that takes a separate integer argument and returns a block that takes two integer arguments and returns a floating-point number. */ float (^func1(int a))(int, int);

    You'll just gain to confidence me when I construe you that this syntax actually makes sense to seasoned C programmers.

    Now then, does this exist necessary that C is suddenly a dynamic, high-level language like JavaScript or Lisp? Hardly. The existing distinction between the stack and the heap, the rules governing automatic and static variables, and so on are whole soundless in full effect. Plus, now there's a whole recent set of rules for how blocks interact with each of these things. There's even a recent __block storage character ascribe to further control the scope and lifetime of values used in blocks.

    All of that said, blocks are soundless a huge win in C. Thanks to blocks, the friendlier APIs long enjoyed by dynamic languages are now feasible in C-derived languages. For example, suppose you want to apply some operation to every line in a file. To effect so in a low-level language like C requires some amount of boilerplate code to open and read from the file, wield any errors, read each line into a buffer, and antiseptic up at the end.

    FILE *fp = fopen(filename, "r"); if (fp == NULL) { perror("Unable to open file"); } else { char line[MAX_LINE]; while (fgets(line, MAX_LINE, fp)) { work; work; work; } fclose(fp); }

    The portion in bold is an abstract representation of what you're planning to effect to each line of the file. The relaxation is the literal boilerplate code. If you find yourself having to apply varying operations to every line of many different files, this boilerplate code gets tedious.

    What you'd like to exist able to effect is factor it out into a duty that you can call. But then you're faced with the problem of how to express the operation you'd like to effect on each line of the file. In the middle of each block of boilerplate may exist many lines of code expressing the operation to exist applied. This code may reference or modify local variables which are affected by the runtime conduct of the program, so traditional duty pointers won't work. What to do?

    Thanks to blocks, you can define a duty that takes a filename and a block as arguments. This gets whole the uninteresting code out of your face.

    foreach_line(filename, ^ (char *line) { work; work; work; });

    What's left is a much clearer expression of your intent, with less surrounding noise. The argument after filename is a literal block that takes a line of text as an argument.

    Even when the volume of boilerplate is small, the simplicity and clarity premium is soundless worthwhile. consider the simplest feasible loop that executes a fixed number of times. In C-based languages, even that basic construct offers a surprising number of opportunities for bugs. Let's do_something() 10 times:

    for (int i = 0; i <= 10; i++) { do_something(); }

    Oops, I've got a slight bug there, don't I? It happens to the best of us. But why should this code exist more complicated than the sentence describing it. effect something 10 times! I never want to screw that up again. Blocks can help. If they just invest a slight endeavor up front to define a helper function:

    typedef void (^work_t)(void); void repeat(int n, work_t block) { for (int i = 0; i < n; ++i) block(); }

    We can banish the bug for good. Now, repeating any arbitrary block of code a specific number of times is whole but idiot-proof:

    repeat(10, ^{ do_something() }); repeat(20, ^{ do_other_thing() });

    And remember, the block argument to repeat() can contain exactly the identical kindly of code, literally copied and pasted, that would gain appeared within a traditional for loop.

    All these possibilities and more gain been well explored by dynamic languages: map, reduce, collect, etc. Welcome, C programmers, to a higher order.

    Apple has taken these lessons to heart, adding over 100 recent APIs that exercise blocks in Snow Leopard. Many of these APIs would not exist feasible at whole without blocks, and whole of them are more elegant and concise than they would exist otherwise.

    It's Apple remonstrate to submit blocks as an official extension to one or more of the C-based languages, though it's not yet pellucid which standards bodies are receptive to the proposal. For now, blocks are supported by whole four of Apple's compilers in Mac OS X.

    Concurrency in the real world: a prelude

    The struggle to construct efficient exercise of a large number of independent computing devices is not new. For decades, the field of high-performance computing has tackled this problem. The challenges faced by people writing software for supercomputers many years ago gain now trickled down to desktop and even mobile computing platforms.

    In the PC industry, some people saw this coming earlier than others. Almost 20 years ago, exist Inc. was formed around the understanding of creating a PC platform unconstrained by legacy limitations and entirely prepared for the coming abundance of independent computing units on the desktop. To that end, exist created the BeBox, a dual-CPU desktop computer, and BeOS, a brand-new operating system.

    The signature ensnare phrase for BeOS was "pervasive multithreading." The BeBox and other machines running BeOS leveraged every ounce of the diminutive (by today's standards, anyway) computing resources at their disposal. The demos were impressive. A dual 66 MHz machine (don't construct me point to another graph) could play multiple videos simultaneously while besides playing several audio tracks from a CD—some backwards— and whole the while, the user interface remained completely responsive.

    Let me construe you, having lived through this age myself, the undergo was mind-blowing at the time. BeOS created instant converts out of hundreds of technology enthusiasts, many of whom maintain that today's desktop computing undergo soundless doesn't match the responsiveness of BeOS. This is certainly staunch emotionally, if not necessarily literally.

    After nearly purchasing exist in the late 1990s, Apple bought NeXT instead, and the relaxation is history. But had Apple gone with blueprint exist instead, Mac developers might gain had a rough road ahead. While whole that pervasive multithreading made for impressive technology demos and a stately user experience, it could exist extremely demanding on the programmer. BeOS was whole about threads, going so far as to maintain a divide thread for each window. Whether you liked it or not, your BeOS program was going to exist multithreaded.

    Parallel programming is notoriously hard, with the manual management of POSIX-style threads representing the profound immediate of that pool. The best programmers in the world are hard-pressed to create large multithreaded programs in low-level languages like C or C++ without finding themselves impaled on the spikes of deadlock, race conditions, and other perils inherent in the exercise of in multiple simultaneous threads of execution that share the identical recollection space. Extremely watchful application of locking primitives is required to avoid performance-robbing levels of contention for shared data—and the bugs, oh the bugs! The term "Heisenbug" may as well gain been invented for multithreaded programming.

    Nineteen years after exist tilted at the windmill of the widening swath of silicon in desktop PCs, the challenge has only grown. Those transistors are out there, man—more than ever before. Single-threaded programs on today's high-end desktop Macs, even when using "100%" CPU, extend but a separate glowing tower in a sea of sixteen otherwise blank lanes on a CPU monitor window.

    A wide-open  unpretentious of transistorsA wide-open unpretentious of transistors

    And woe exist unto the user if that pegged CPU core is running the main thread of a GUI application on Mac OS X. A CPU-saturated main thread means no recent user inputs are being pulled off the event queue by the application. A few seconds of that and an ancient friend makes its appearance: the spinning beach ball of death.

    Nooooooooo!!!

    Nooooooooo!!! Image from The Iconfactory

    This is the enemy: hardware with more computing resources than programmers know what to effect with, most of it completely idle, and whole the while the user is utterly blocked in his attempts to exercise the current application. What's Snow Leopard's answer? Read on…

    Grand Central Dispatch Apple's GCD branding: <a href="http://en.wikipedia.org/wiki/Foamer">Railfan</a> <a href="http://en.wikipedia.org/wiki/Fan_service">service</a>Apple's GCD branding: Railfan service

    Snow Leopard's respond to the concurrency conundrum is called stately Central Dispatch (GCD). As with QuickTime X, the designation is extremely apt, though this is not entirely pellucid until you understand the technology.

    The first thing to know about GCD is that it's not a recent Cocoa framework or similar special-purpose frill off to the side. It's a unpretentious C library baked into the lowest levels of Mac OS X. (It's in libSystem, which incorporates libc and the other code that sits at the very bottom of userspace.)

    There's no need to link in a recent library to exercise GCD in your program. Just #include <dispatch/dispatch.h> and you're off to the races. The fact that GCD is a C library means that it can exist used from whole of the C-derived languages supported on Mac OS X: Objective-C, C++, and Objective-C++.

    Queues and threads

    GCD is built on a few simple entities. Let's start with queues. A queue in GCD is just what it sounds like. Tasks are enqueued, and then dequeued in FIFO order. (That's "First In, First Out," just like the checkout line at the supermarket, for those who don't know and don't want to succeed the link.) Dequeuing the task means handing it off to a thread where it will execute and effect its actual work.

    Though GCD queues will hand tasks off to threads in FIFO order, several tasks from the identical queue may exist running in parallel at any given time. This animation demonstrates.

    A stately Central Dispatch queue in action

    You'll notice that task B completed before task A. Though dequeuing is FIFO, task completion is not. besides note that even though there were three tasks enqueued, only two threads were used. This is an necessary feature of GCD which we'll argue shortly.

    But first, let's stare at the other kindly of queue. A serial queue works just like a middling queue, except that it only executes one task at a time. That means task completion in a serial queue is besides FIFO. Serial queues can exist created explicitly, just like middling queues, but each application besides has an implicit "main queue" which is a serial queue that runs on the main thread.

    The animation above shows threads appearing as labor needs to exist done, and disappearing as they're no longer needed. Where effect these threads approach from and where effect they Go when they're done? GCD maintains a global pool of threads which it hands out to queues as they're needed. When a queue has no more pending tasks to rush on a thread, the thread goes back into the pool.

    This is an extremely necessary aspect of GCD's design. Perhaps surprisingly, one of the most difficult parts of extracting maximum performance using traditional, manually managed threads is figuring out exactly how many threads to create. Too few, and you risk leaving hardware idle. Too many, and you start to disburse a significant amount of time simply shuffling threads in and out of the available processor cores.

    Let's Tell a program has a problem that can exist split into eight separate, independent units of work. If this program then creates four threads on an eight-core machine, is this an instance of creating too many or too few threads? Trick question! The respond is that it depends on what else is happening on the system.

    If six of the eight cores are totally saturated doing some other work, then creating four threads will just require the OS to consume time rotating those four threads through the two available cores. But wait, what if the process that was saturating those six cores finishes? Now there are eight available cores but only four threads, leaving half the cores idle.

    With the exception of programs that can reasonably anticipate to gain the entire machine to themselves when they run, there's no pass for a programmer to know ahead of time exactly how many threads he should create. Of the available cores on a particular machine, how many are in use? If more become available, how will my program know?

    The bottom line is that the optimal number of threads to attach in flight at any given time is best determined by a single, globally watchful entity. In Snow Leopard, that entity is GCD. It will preserve zero threads in its pool if there are no queues that gain tasks to run. As tasks are dequeued, GCD will create and dole out threads in a pass that optimizes the exercise of the available hardware. GCD knows how many cores the system has, and it knows how many threads are currently executing tasks. When a queue no longer needs a thread, it's returned to the pool where GCD can hand it out to another queue that has a task ready to exist dequeued.

    There are further optimizations inherent in this scheme. In Mac OS X, threads are relatively heavyweight. Each thread maintains its own set of register values, stack pointer, and program counter, plus kernel data structures tracking its security credentials, scheduling priority, set of pending signals and signal masks, etc. It whole adds up to over 512 KB of overhead per thread. Create a thousand threads and you've just burned about a half a gigabyte of recollection and kernel resources on overhead alone, before even considering the actual data within each thread.

    Compare a thread's 512 KB of baggage with GCD queues which gain a mere 256 bytes of overhead. Queues are very lightweight, and developers are encouraged to create as many of them as they need—thousands, even. In the earlier animation, when the queue was given two threads to process its three tasks, it executed two tasks on one of the threads. Not only are threads heavyweight in terms of recollection overhead, they're besides relatively costly to create. Creating a recent thread for each task would exist the worst feasible scenario. Every time GCD can exercise a thread to execute more than one task, it's a win for overall system efficiency.

    Remember the problem of the programmer trying to design out how many threads to create? Using GCD, he doesn't gain to worry about that at all. Instead, he can concentrate entirely on the optimal concurrency of his algorithm in the abstract. If the best-case scenario for his problem would exercise 500 concurrent tasks, then he can Go ahead and create 500 GCD queues and dole his labor among them. GCD will design out how many actual threads to create to effect the work. Furthermore it will adjust the number of threads dynamically as the conditions on the system change.

    But perhaps most importantly, as recent hardware is released with more and more CPU cores, the programmer does not need to change his application at all. Thanks to GCD, it will transparently consume handicap of any and whole available computing resources, up to—but not past!—the optimal amount of concurrency as originally defined by the programmer when he chose how many queues to create.

    But wait, there's more! GCD queues can actually exist arranged in arbitrarily complex directed acyclic graphs. (Actually, they can exist cyclic too, but then the conduct is undefined. Don't effect that.) Queue hierarchies can exist used to funnel tasks from disparate subsystems into a narrower set of centrally controlled queues, or to accommodate a set of middling queues to delegate to a serial queue, effectively serializing them whole indirectly.

    There are besides several levels of priority for queues, dictating how often and with what urgency threads are distributed to them from the pool. Queues can exist suspended, resumed, and cancelled. Queues can besides exist grouped, allowing whole tasks distributed to the group to exist tracked and accounted for as a unit.

    Overall, GCD's exercise of queues and threads forms a simple, elegant, but besides extremely pragmatic architecture.

    Asynchronicity

    Okay, so GCD is a stately pass to construct efficient exercise of the available hardware. But is it really any better than BeOS's approach to multithreading? We've already seen a few ways that GCD avoids the pitfalls of BeOS (e.g., the reuse of threads and the maintenance of a global pool of threads that's correctly sized for the available hardware). But what about the problem of overwhelming the programmer by requiring threads in places where they complicate, rather than enhance the application?

    GCD embodies a philosophy that is at the contrary immediate of the spectrum from BeOS's "pervasive multithreading" design. Rather than achieving responsiveness by getting every feasible component of an application running concurrently on its own thread (and paying a cumbersome charge in terms of complex data sharing and locking concerns), GCD encourages a much more limited, hierarchical approach: a main application thread where whole the user events are processed and the interface is updated, and worker threads doing specific jobs as needed.

    In other words, GCD doesn't require developers to reason about how best to split the labor of their application into multiple concurrent threads (though when they're ready to effect that, GCD will exist willing and able to help). At its most basic level, GCD aims to hearten developers to coast from thinking synchronously to thinking asynchronous. Something like this: "Write your application as usual, but if there's any portion of its operation that can reasonably exist expected to consume more than a few seconds to complete, then for the savor of Zarzycki, obtain it off the main thread!"

    That's it; no more, no less. Beach ball banishment is the cornerstone of user interface responsiveness. In some respects, everything else is gravy. But most developers know this intuitively, so why effect they soundless perceive the beach ball in Mac OS X applications? Why don't whole applications already execute whole of their potentially long-running tasks on background threads?

    A few reasons gain been mentioned already (e.g., the rigor of knowing how many threads to create) but the mountainous one is much more pragmatic. Spinning off a thread and collecting its result has always been a bit of a pain. It's not so much that it's technically difficult, it's just that it's such an specific crash from coding the actual labor of your application to coding whole this task-management plumbing. And so, especially in borderline cases, like an operation that may consume 3 to 5 seconds, developers just effect it synchronously and coast onto the next thing.

    Unfortunately, there's a surprising number of very common things that an application can effect that execute quickly most of the time, but gain the potential to consume much longer than a few seconds when something goes wrong. Anything that touches the file system may stall at the lowest levels of the OS (e.g., within blocking read() and write() calls) and exist matter to a very long (or at least an "unexamined-by-the-application-developer") timeout. The identical goes for designation lookups (e.g., DNS or LDAP), which almost always execute instantly, but ensnare many applications completely off-guard when they start taking their sweet time to return a result. Thus, even the most meticulously constructed Mac OS X applications can immediate up throwing the beach ball in their puss from time to time.

    With GCD, Apple is proverb it doesn't gain to exist this way. For example, suppose a document-based application has a button that, when clicked, will analyze the current document and panoply some intriguing statistics about it. In the common case, this analysis should execute in under a second, so the following code is used to connect the button with an action:

    - (IBAction)analyzeDocument:(NSButton *)sender { NSDictionary *stats = [myDoc analyze]; [myModel setDict:stats]; [myStatsView setNeedsDisplay:YES]; [stats release]; }

    The first line of the duty body analyzes the document, the second line updates the application's internal state, and the third line tells the application that the statistics view needs to exist updated to reflect this recent state. It whole follows a very common pattern, and it works stately as long as not a soul of these steps—which are whole running on the main thread, remember—takes too long. Because after the user presses the button, the main thread of the application needs to wield that user input as hasty as feasible so it can obtain back to the main event loop to process the next user action.

    The code above works stately until a user opens a very large or very complex document. Suddenly, the "analyze" step doesn't consume one or two seconds, but 15 or 30 seconds instead. Hello, beach ball. And still, the developer is likely to hem and haw: "This is really an exceptional situation. Most of my users will never open such a large file. And anyway, I really don't want to start reading documentation about threads and adding whole that extra code to this simple, four-line function. The plumbing would dwarf the code that does the actual work!"

    Well, what if I told you that you could coast the document analysis to the background by adding just two lines of code (okay, and two lines of closing braces), whole located within the existing function? No application-global objects, no thread management, no callbacks, no argument marshalling, no context objects, not even any additional variables. Behold, stately Central Dispatch:

    - (IBAction)analyzeDocument:(NSButton *)sender { dispatch_async(dispatch_get_global_queue(0, 0), ^{ NSDictionary *stats = [myDoc analyze]; dispatch_async(dispatch_get_main_queue(), ^{ [myModel setDict:stats]; [myStatsView setNeedsDisplay:YES]; [stats release]; }); }); }

    There's a hell of a lot of packed into those two lines of code. whole of the functions in GCD commence with dispatch_, and you can perceive four such calls in the blue lines of code above. The key to the minimal invasiveness of this code is revealed in the second argument to the two dispatch_async() calls. Thus far, I've been discussing "units of work" without specifying how, exactly, GCD models such a thing. The answer, now revealed, should seem obvious in retrospect: blocks! The faculty of blocks to capture the surrounding context is what allows these GCD calls to exist dropped privilege into some existing code without requiring any additional setup or re-factoring or other contortions in service of the API.

    But the best portion of this code is how it deals with the problem of detecting when the background task completes and then showing the result. In the synchronous code, the analyze manner muster and the code to update the application panoply simply exhibit in the desired sequence within the function. In the asynchronous code, miraculously, this is soundless the case. Here's how it works.

    The outer dispatch_async() muster puts a task on a global concurrent GCD queue. That task, represented by the block passed as the second argument, contains the potentially time-consuming analyze manner call, plus another muster to dispatch_async() that puts a task onto the main queue—a serial queue that runs on the main thread, remember—to update the application's user interface.

    User interface updates must whole exist done from the main thread in a Cocoa application, so the code in the inner block could not exist executed anywhere else. But rather than having the background thread transmit some kindly of special-purpose notification back to the main thread when the analyze manner muster completes (and then adding some code to the application to detect and wield this notification), the labor that needs to exist done on the main thread to update the panoply is encapsulated in yet another block within the larger one. When the analyze muster is done, the inner block is attach onto the main queue where it will (eventually) rush on the main thread and effect its labor of updating the display.

    Simple, elegant, and effective. And for developers, no more excuses.

    Believe it or not, it's just as smooth to consume a serial implementation of a chain of independent operations and parallelize it. The code below does labor on import elements of data, one after the other, and then summarizes the results once whole the elements gain been processed.

    for (i = 0; i < count; i++) { results[i] = do_work(data, i); } total = summarize(results, count);

    Now here's the parallel version which puts a divide task for each element onto a global concurrent queue. (Again, it's up to GCD to select how many threads to actually exercise to execute the tasks.)

    dispatch_apply(count, dispatch_get_global_queue(0, 0), ^(size_t i) { results[i] = do_work(data, i); }); total = summarize(results, count);

    And there you gain it: a for loop replaced with a concurrency-enabled equivalent with one line of code. No preparation, no additional variables, no impossible decisions about the optimal number of threads, no extra labor required to wait for whole the independent tests to complete. (The dispatch_apply() muster will not return until whole the tasks it has dispatched gain completed.) Stunning.

    Grand Central Awesome

    Of whole the APIs added in Snow Leopard, stately Central Dispatch has the most far-reaching implications for the future of Mac OS X. Never before has it been so smooth to effect labor asynchronously and to spread workloads across many CPUs.

    When I first heard about stately Central Dispatch, I was extremely skeptical. The greatest minds in computer science gain been working for decades on the problem of how best to extract parallelism from computing workloads. Now here was Apple apparently promising to solve this problem. Ridiculous.

    But stately Central Dispatch doesn't actually address this issue at all. It offers no abet whatsoever in deciding how to split your labor up into independently executable tasks—that is, deciding what pieces can or should exist executed asynchronously or in parallel. That's soundless entirely up to the developer (and soundless a tough problem). What GCD does instead is much more pragmatic. Once a developer has identified something that can exist split off into a divide task, GCD makes it as smooth and non-invasive as feasible to actually effect so.

    The exercise of FIFO queues, and especially the existence of serialized queues, seems counter to the spirit of ubiquitous concurrency. But we've seen where the Platonic example of multithreading leads, and it's not a pleasant status for developers.

    One of Apple's slogans for stately Central Dispatch is "islands of serialization in a sea of concurrency." That does a stately job of capturing the practical reality of adding more concurrency to run-of-the-mill desktop applications. Those islands are what insulate developers from the thorny problems of simultaneous data access, deadlock, and other pitfalls of multithreading. Developers are encouraged to identify functions of their applications that would exist better executed off the main thread, even if they're made up of several sequential or otherwise partially interdependent tasks. GCD makes it smooth to crash off the entire unit of labor while maintaining the existing order and dependencies between subtasks.

    Those with some multithreaded programming undergo may exist unimpressed with the GCD. So Apple made a thread pool. mountainous deal. They've been around forever. But the angels are in the details. Yes, the implementation of queues and threads has an elegant simplicity, and baking it into the lowest levels of the OS really helps to lower the perceived barrier to entry, but it's the API built around blocks that makes stately Central Dispatch so attractive to developers. Just as Time Machine was "the first backup system people will actually use," stately Central Dispatch is poised to finally spread the heretofore gloomy expertise of asynchronous application design to whole Mac OS X developers. I can't wait.

    OpenCL Somehow, OpenCL got in on the <a href="http://arstechnica.com/apple/2007/10/mac-os-x-10-5/8/#core-spheres">"core" branding</a>Somehow, OpenCL got in on the "core" branding

    So far, we've seen a few examples of doing more with more: a new, more modern compiler infrastructure that supports an necessary recent language feature, and a powerful, pragmatic concurrency API built on top of the recent compilers' advocate for said language feature. whole this goes a long pass towards helping developers and the OS itself construct maximum exercise of the available hardware.

    But CPUs are not the only components experiencing a glut of transistors. When it comes to the proliferation of independent computation engines, another piece of silicon inside every Mac is the undisputed title holder: the GPU.

    The numbers construe the tale. While Mac CPUs contain up to four cores (which may point to up as eight rational cores thanks to symmetric multithreading), high-end GPUs contain well over 200 processor cores. While CPUs are just now edging over 100 GFLOPS, the best GPUs are capable of over 1,000 GFLOPS. That's one trillion floating-point operations per second. And like CPUs, GPUs now approach more than one on a board.

    Writing for the GPU

    Unfortunately, the cores on a GPU are not general-purpose processors (at least not yet). They're much simpler computing engines that gain evolved from the fixed-function silicon of their ancestors that could not exist programmed directly at all. They don't advocate the rich set of instructions available on CPUs, the maximum size of the programs that will rush is often limited and very small, and not whole of the features of the industry-standard IEEE floating-point computation specification are supported.

    Today's GPUs can exist programmed, but the most common forms of programmability are soundless firmly planted in the world of graphics programming: vertex shaders, geometry shaders, pixel shaders. Most of the languages used to program GPUs are similarly graphically focused: HLSL, GLSL, Cg.

    Nevertheless, there are computational tasks outside the realm of graphics that are a superior fit for GPU hardware. It would exist nice if there were a non-graphics-oriented language to write them in. Creating such a thing is quite a challenge, however. GPU hardware varies wildly in every imaginable way: number and character of execution units, available data formats, instruction sets, recollection architecture, you designation it. Programmers don't want to exist exposed to these differences, but it's difficult to labor around the complete lack of a feature or the unavailability of a particular data type.

    GPU vendor NVIDIA gave it a shot, however, and produced CUDA: a subset of the C language with extensions for vector data types, data storage specifiers that reflect typical GPU recollection hierarchy, and several bundled computational libraries. CUDA is but one entrant in the burgeoning GPGPU field (General-Purpose computing on Graphics Processing Units). But coming from a GPU vendor, it faces an uphill battle with developers who really want a vendor-agnostic solution.

    In the world of 3D programming, OpenGL fills that role. As you've surely guessed by now, OpenCL aims to effect the identical for general-purpose computation. In fact, OpenCL is supported by the identical consortium as OpenGL: the ominously named Khronos Group. But construct no mistake, OpenCL is Apple's baby.

    Apple understood that OpenCL's best random of success was to become an industry standard, not just an Apple technology. To construct that happen, Apple needed the cooperation of the top GPU vendors, plus an agreement with an established, widely-recognized standards body. It took a while, but now it's whole approach together.

    OpenCL is a lot like CUDA. It uses a C-like language with the vector extensions, it has a similar model of recollection hierarchy, and so on. This is no surprise, considering how closely Apple worked with NVIDIA during the evolution of OpenCL. There's besides no pass any of the mountainous GPU vendors would radically alter their hardware to advocate an as-yet-unproven standard, so OpenCL had to labor well with GPUs already designed to advocate CUDA, GLSL, and other existing GPU programming languages.

    The OpenCL difference

    This is whole well and good, but to gain any impact on the day-to-day life of Mac users, developers actually gain to exercise OpenCL in their applications. Historically, GPGPU programming languages gain not seen much exercise in traditional desktop applications. There are several reasons for this.

    Early on, writing programs for the GPU often required the exercise of vendor-specific assembly languages that were far removed from the undergo of writing a typical desktop application using a concomitant GUI API. The more C-like languages that came later remained either graphics-focused, vendor-specific, or both. Unless running code on the GPU would accelerate a core component of an application by an order of magnitude, most developers soundless could not exist bothered to navigate this exotic world.

    And even if the GPU did give a huge speed boost, relying on graphics hardware for general-purpose computation was very likely to narrow the potential audience for an application. Many older GPUs, especially those organize in laptops, cannot rush languages like CUDA at all.

    Apple's key determination in the design of OpenCL was to allow OpenCL programs to rush not just on GPUs, but on CPUs as well. An OpenCL program can query the hardware it's running on and enumerate whole eligible OpenCL devices, categorized as CPUs, GPUs, or dedicated OpenCL accelerators (the IBM Cell Blade server—yes, that Cell—is apparently one such device). The program can then dispatch its OpenCL tasks to any available device. It's besides feasible to create a separate rational device consisting of any combination of eligible computing resources: two GPUs, a GPU and two CPUs, etc.

    The advantages of being able to rush OpenCL programs on both CPUs and GPUs are obvious. Every Mac running Snow Leopard, not just those with the recent-model GPUs, can rush a program that contains OpenCL code. But there's more to it than that.

    Certain kinds of algorithms actually rush faster on high-end multi-core CPUs than on even the very fastest available GPUs. At WWDC 2009, an engineer from Electronic Arts demonstrated an OpenCL port of a skinning engine from one of its games running over four times faster on a four-core Mac Pro than on an NVIDIA GeForce GTX285. Restructuring the algorithm and making many other changes to better suit the limitations (and strengths) of the GPU pushed it back ahead of the CPU by a wide margin, but sometimes you just want the system you gain to rush well as-is. Being able to target the CPU is extremely useful in those cases.

    Moreover, writing vector code for Intel CPUs "the old-fashioned way" can exist a real pain. There's MMX, SSE, SSE2, SSE3, and SSE4 to deal with, whole with slightly different capabilities, and whole of which accommodate the programmer to write code like this:

    r1 = _mm_mul_ps(m1, _mm_add_ps(x1, x2));

    OpenCL's indigenous advocate for vector types de-clutters the code considerably:

    r1 = m1 * (x1 + x2);

    Similarly, OpenCL's advocate for implicit parallelism makes it much easier to consume handicap of multiple CPU cores. Rather than writing whole the logic to split your data into pieces and dole those pieces to the parallel-computing hardware, OpenCL lets you write just the code to operate on a separate piece of the data and then transmit it, along with the entire block of data and the desired flat of parallelism, to the computing device.

    This arrangement is taken for granted in traditional graphics programming, where code implicitly works on whole pixels in a texture or whole vertices in a polygon; the programmer only needs to write code that will exist in the "inner loop," so to speak. An API with advocate for this kindly of parallelism that runs on CPUs as well as GPUs fills an necessary gap.

    Writing to OpenCL besides future-proofs task- or data-parallel code. Just as the identical OpenGL code will obtain faster and faster as newer, more powerful GPUs are released, so too will OpenCL code effect better as CPUs and GPUs obtain faster. The extra layer of abstraction that OpenCL provides makes this possible. For example, though vector code written several years ago using MMX got faster as CPU clock speeds increased, a more significant performance boost likely requires porting the code to one of the newer SSE instruction sets.

    As newer, more powerful vector instruction sets and parallel hardware becomes available, Apple will update its OpenCL implementations to consume handicap of them, just as video card makers and OS vendors update their OpenGL drivers to consume handicap of faster GPUs. Meanwhile, the application developer's code remains unchanged. Not even a recompile is required.

    Here exist dragons (and trains)

    How, you may wonder, can the identical compiled code immediate up executing using SSE2 on one machine and SSE4 on another, or on an NVIDIA GPU on one machine and an ATI GPU on another? To effect so would require translating the device-independent OpenCL code to the instruction set of the target computing device at runtime. When running on a GPU, OpenCL must besides ship the data and the newly translated code over to the video card and collect the results at the end. When running on the CPU, OpenCL must disarrange for the requested flat of parallelism by creating and distributing threads appropriately to the available cores.

    Well, wouldn't you know it? Apple just happens to gain two technologies that solve these exact problems.

    Want to compile code "just in time" and ship it off to a computing device? That's what LLVM was born to do—and, indeed, what Apple did with it in Leopard, albeit on a more limited scale. OpenCL is a natural extension of that work. LLVM allows Apple to write a separate code generator for each target instruction set, and concentrate whole of its endeavor on a separate device-independent code optimizer. There's no longer any need to duplicate these tasks, using one compiler to create the static application executable and having to jury-rig another for just-in-time compilation.

    (Oh, and by the way, bethink Core Image? That's another API that needs to compile code just-in-time and ship it off to execute on parallel hardware like GPUs and multi-core CPUs. In Snow Leopard, Core Image has been re-implemented using OpenCL, producing a hefty 25% overall performance boost.)

    To wield task parallelism and provision threads, OpenCL is built on top of stately Central Dispatch. This is such a natural fit that it's a bit surprising that the OpenCL API doesn't exercise blocks. I reason Apple decided that it shouldn't press its luck when it comes to getting its home-grown technologies adopted by other vendors. This determination already seems to exist paying off, as AMD has its own OpenCL implementation under way.

    The top of the pyramid

    Though the underlying technologies, Clang, blocks and stately Central Dispatch, will undoubtedly exist more widely used by developers, OpenCL represents the culmination of that particular technological thread in Snow Leopard. This is the gold criterion of software engineering: creating a recent public API by edifice it on top of lower-level, but equally well-designed and implemented public APIs.

    A unified abstraction for the ever-growing heterogeneous collection of parallel computing silicon in desktop computers was sorely needed. We've got an increasing population of powerful CPU cores, but they soundless exist in numbers that are orders of magnitude lower than the hundreds of processing units in modern GPUs. On the other hand, GPUs soundless gain a ways to Go to ensnare up with the power and flexibility of a full-fledged CPU core. But even with whole the differences, writing code exclusively for either one of those worlds soundless smacks of leaving money on the table.

    With OpenCL in hand, there's no longer a need to attach whole your eggs in one silicon basket. And with the advent of hybrid CPU/GPU efforts like Intel's Larabee, which exercise CPU-caliber processing engines, but in much higher numbers, OpenCL may prove even more necessary in the coming years.

    Transistor harvest

    Collectively, the concurrency-enabling features introduced in Snow Leopard picture the biggest boost to asynchronous and parallel software evolution in any Mac OS X release—perhaps in any desktop operating system release ever. It may exist hard for end-users to obtain excited about "plumbing" technologies like stately Central Dispatch and OpenCL, let solitary compilers and programming language features, but it's upon these foundations that developers will create ever-more-impressive edifices of software. And if those applications tower over their synchronous, serial predecessors, it will exist because they stand on the shoulders of giants.

    QuickTime Player's  recent icon (Not a fan)QuickTime Player's recent icon (Not a fan) QuickTime Player

    There's been some confusion surrounding QuickTime in Snow Leopard. The earlier section about QuickTime X explains what you need to know about the present and future of QuickTime as a technology and an API. But a few of Apple's decisions—and the extremely overloaded meaning of the word "QuickTime" in the minds of consumers—have blurred the picture somewhat.

    The first head-scratcher occurs during installation. If you befall to click on the "Customize…" button during installation, you'll perceive the following options:

    QuickTime 7 is an optional install?QuickTime 7 is an optional install?

    We've already talked about Rosetta being an optional install, but QuickTime 7 too? Isn't QuickTime severely crippled without QuickTime 7? Why in the world would that exist an optional install?

    Well, there's no need to panic. That detail in the installer should actually read "QuickTime Player 7." QuickTime 7, the ancient but extremely capable media framework discussed earlier, is installed by default in Snow Leopard—in fact, it's mandatory. But the player application, the one with the ancient blue "Q" icon, the one that many casual users actually reason of as being "QuickTime," that's been replaced with a recent QuickTime-X-savvy version sporting a pudgy recent icon (see above right).

    The recent player application is a mountainous departure from the old. Obviously, it leverages QuickTime X for more efficient video playback, but the user interface is besides completely new. Gone are the gray edge and bottom-mounted playback controls from the ancient QuickTime Player, replaced by a frameless window with a black title bar and a floating, moveable set of controls.

    The  recent QuickTime Player: boldly going where <a href="http://code.google.com/p/niceplayer/">NicePlayer</a> has gone before Enlarge / The recent QuickTime Player: boldly going where NicePlayer has gone before

    It's like a combination of the window treatment of the excellent NicePlayer application and the full-screen playback controls from the ancient QuickTime Player. I'm a bit bothered by two things. First, the ever-so-slightly clipped corners seem like a evil idea. Am I just suppositious to give up those dozen-or-so pixels? NicePlayer does it right, showing crisp, square corners.

    Second, the floating playback controls obscure the movie. What if I'm scrubbing around looking for something in that portion of the frame? Yes, you can coast the controls, but what if I'm looking for something in an unknown location in the frame? Also, the title bar obscures an entire swath of the top of the frame, and this can't exist moved. I value the compactness of this approach, but it'd exist nice if the title bar overlap could exist disabled and the controls could exist dragged off the movie entirely and docked to the bottom or something.

    (One blessing for people who share my OCD tendencies: if you coast the floating controls, they don't bethink their position the next time you open a movie. Why is that a blessing? Because if it worked the other way, we'd whole disburse pass too much time fretting about their inability to restore the controller to its default, precisely centered position. Sad, but true.)

    The recent QuickTime Player presents a decidedly iMovie-like (or is it iPhone-like, nowadays?) interface for trimming video. Still-frame thumbnails are placed side-by-side to form a timeline, with adjustable stops at each immediate for trimming.

    Trimming in the  recent QuickTime Player Enlarge / Trimming in the recent QuickTime Player

    Holding down the option key changes from a thumbnail timeline to an audio waveform display:

    Trimming with audio waveform view Enlarge / Trimming with audio waveform view

    In both the video and audio cases, I gain to marvel exactly how useful the fancy timeline appearances are. The audio waveform is quite wee and compressed, and the limited horizontal space of the in-window panoply means a movie can only point to a handful of video frames in its timeline. Also, if there's any faculty to effect fine adjustments using something other than extremely watchful mouse movements (which are necessarily matter to a limited resolution) then I couldn't find it. Final nick Pro this is not.

    QuickTime Player has erudite another recent trick: screen recording. The controls are limited, so more demanding users will soundless gain a need for a full-featured screen recorder, but QuickTime Player gets the job done.

    Screen recording in QuickTime PlayerScreen recording in QuickTime Player

    There's besides an audio-only option, with a similarly simplified collection of settings.

    Audio recordingAudio recording

    Finally, the recent QuickTime Player has the faculty to upload a movie directly to YouTube and MobileMe, transmit one via e-mail, or add it to your iTunes library. The export options are besides vastly simplified, with preset options for iPhone/iPod, Apple TV, and HD 480p and 720p.

    Unfortunately, the list of things you can't effect with the recent QuickTime Player is quite long. You can't cut, copy, and paste arbitrary portions of a movie (trimming only affects the ends); you can't extract or delete individual tracks or overlay one track onto another (optionally scaling to fit); you can't export a movie by choosing from the full set of available QuickTime audio and video codecs. whole of these things were feasible with the ancient QuickTime Player—if, that is, you paid the $30 for a QuickTime Pro license. In the past, I've described this extra fee as "criminally stupid", but the features it enabled in QuickTime Player were really useful.

    It's tempting to ascribe their absence in the recent QuickTime Player to the previously discussed limitations of QuickTime X. But the recent QuickTime Player is built on top of QTKit, which serves as a front-end for both QuickTime X and QuickTime 7. And it does, after all, feature some limited editing features like trimming, plus some previously "Pro"-only features like full-screen playback. Also, the recent QuickTime Player can indeed play movies using third-party plug-ins—a feature clearly powered by QuickTime 7.

    Well, Snow Leopard has an extremely pleasant flabbergast waiting for you if you install the optional QuickTime Player 7. When I did so, what I got was the ancient QuickTime Player—somewhat insultingly installed in the "Utilities" folder—with whole of its "Pro" features permanently unlocked. Yes, the tyranny of QuickTime Pro seems to exist at an end…

    QuickTime Pro: now free for everyone?QuickTime Pro: now free for everyone?

    …but perhaps the key word above is "seems," because QuickTime Player 7 does not gain whole "pro" features unlocked for everyone. I installed Snow Leopard onto an blank disk, and QuickTime 7 was not automatically installed (as it is when the installer detects an existing QuickTime Pro license on the target disk). After booting from my fresh Snow Leopard volume, I manually installed the "QuickTime 7" optional component using the Snow Leopard installer disk.

    The result for me was a QuickTime Player 7 application with whole pro features unlocked and with no visible QuickTime Pro registration information. I did, however, gain a QuickTime Pro license on one of the attached drives. Apparently, the installer detected this and gave me an unlocked QuickTime Player 7 application, even though the boot volume never had a QuickTime Pro license on it.

    The Dock

    The recent appearance of some aspects of the Dock are accompanied by some recent functionality as well. Clicking and holding on a running application's Dock icon now triggers Expos�, but only for the windows belonging to that application. Dragging a file onto a docked application icon and holding it there for a bit produces the identical result. You can then continue that identical drag onto one of the Exposé window thumbnails and hover there a bit to bring that window to the front and drop the file into it. It's a pretty handy technique, once you obtain in the usage of doing it.

    The Exposé panoply itself is besides changed. Now, minimized windows are displayed in smaller form on the bottom of the screen below a thin line.

    Dock Exposé with  recent placement of minimized windows Enlarge / Dock Exposé with recent placement of minimized windows

    In the screenshot above, you'll notice that not a soul of the minimized windows exhibit in my Dock. That's thanks to another welcome addition: the faculty to minimize windows "into" the application icon. You'll find the setting for this in the Dock's preference pane.

    New Dock preference: Minimize windows into application iconNew Dock preference: Minimize windows into application icon Minimized windows in a Dock application menuMinimized window denoted by a diamond

    Once set, minimized windows will slip behind the icon of their parent application and then disappear. To obtain them back, either right-click the application icon (see right) or trigger Exposé.

    The Dock's grid view for folders now incorporates a scroll bar when there are too many items to fit comfortably. Clicking on a folder icon in the grid now shows that folder's contents within the grid, allowing you to navigate down several folders to find a buried item. A wee "back" navigation button appears once you descend.

    These are whole useful recent behaviors, and quite a premium considering the suppositious "no recent features" stance of Snow Leopard. But the fundamental nature of the Dock remains the same. Users who want a more supple or more powerful application launcher/folder organizer/window minimization system must soundless either sacrifice some functionality (e.g., Dock icon badges and bounce notifications) or continue to exercise the Dock in addition to a third-party application.

    The option to preserve minimized windows from cluttering up the Dock was long overdue. But my enthusiasm is tempered by my frustration at the continued inability to click on a docked folder and gain it open in the Finder, while besides retaining the faculty to drag items into that folder. This was the default conduct for docked folders for the first six years of Mac OS X's life, but it changed in Leopard. Snow Leopard does not better matters.

    Docking an alias to a folder provides the single-click-open behavior, but items cannot exist dragged into a docked folder alias for some inexplicable reason. (Radar 5775786, closed in March 2008 with the terse explanation, "not currently supported.") Worse, dragging an detail to a docked folder alias looks like it will labor (the icon highlights) but upon release, the dragged detail simply springs back to its original location. I really hoped this one would obtain fixed in Snow Leopard. No such luck.

    Dock grid view's in-place navigation with back buttonDock grid view's in-place navigation with back button The Finder

    One of the earliest leaked screenshots of Snow Leopard included an innocuous-looking "Get Info…" window for the Finder, presumably to point to that its version number had been updated to 10.6. The more intriguing tidbit of information it revealed was that the Finder in Snow Leopard was a 64-bit application.

    The Mac OS X Finder started its life as the designated "dog food" application for the Carbon backward-compatibility API for Mac OS X. Over the years, the Finder has been a frequent target of dissatisfaction and scorn. Those evil feelings frequently spilled over into the parallel debate over API supremacy: Carbon vs. Cocoa.

    "The Finder sucks because it's a Carbon app. What they need is a Cocoa Finder! Surely that will solve whole their woes." Well, Snow Leopard features a 64-bit Finder, and as they whole know, Carbon was not ported to 64-bit. Et voila! A Cocoa Finder in Snow Leopard. (More on the woes in a bit.)

    The conversion to Cocoa followed the Snow Leopard formula: no recent features… except for maybe one or two. And so, the "new" Cocoa Finder looks and works almost exactly like the ancient Carbon Finder. The biggest indicator of its "Cocoa-ness" is the extensive exercise of Core Animation transitions. For example, when a Finder window does its schizophrenic transformation from a sidebar-bedecked browser window to its minimally-adorned form, it no longer happens in a blink. Instead, the sidebar slides away and fades, the toolbar shrinks, and everything tucks in to form its recent shape.

    Despite crossing the line in a few cases, the Core Animation transitions effect construct the application feel more polished, and yes, "more Cocoa." And presumably the exercise of Cocoa made it so darn smooth to add features that the developers just couldn't resist throwing in a few.

    The number-one feature request from cumbersome column-view users has finally been implemented: sortable columns. The sort order applies to whole columns at once, which isn't as nice as per-column sorting, but it's much better than nothing at all. The sort order can exist set using a menu command (each of which has a keyboard shortcut) or by right-clicking in an unoccupied locality of a column and selecting from the resulting context menu.

    Column view sorting context menu Enlarge / Column view sorting context menu Column view sorting menu Enlarge / Column view sorting menu

    Even the lowly icon view has been enhanced in Snow Leopard. Every icon-view window now includes a wee slider to control the size of the icons.

    The Finder's icon view with its  recent slider controlThe Finder's icon view with its recent slider control

    This may seem a bit odd—how often effect people change icon sizes?—but it makes much more sense in the context of previewing images in the Finder. This exercise case is made even more material by the recent expansion of the maximum icon size to 512x512 pixels.

    The icon previews themselves gain been enhanced to better match the abilities available in Quick Look. attach it whole together and you can smoothly zoom a wee PDF icon, for example, into the impressively high-fidelity preview shown below, complete with the faculty to circle pages. One press of the space bar and you'll progress to the even larger and more supple Quick stare view. It's a pretty smooth experience.

    Not your father's icon: 512x512 pixels of multi-page PDF previewingNot your father's icon: 512x512 pixels of multi-page PDF previewing

    QuickTime previews gain been similarly enhanced. As you zoom in on the icon, it transforms into a miniature movie player, adorned with an odd circular progress indicator. Assuming users are willing to wrangle with the vagaries of the Finder's view settings successfully enough to obtain icon view to stick for the windows where it's most useful, I reason that odd slight slider is actually going to obtain a lot of use.

    The Finder's QuickTime preview. (The "glare" overlay is a bit much.)The Finder's QuickTime preview. (The "glare" overlay is a bit much.)

    List view besides has a few enhancements—accidental, incidental, or otherwise. The drag locality for each list view detail now spans the entire line. In Leopard, though the entire line was highlighted, only the file designation or icon portion could exist dragged. Trying to drag anywhere else just extended the selection to other items in the list view as the cursor was moved. I'm not certain whether this change in conduct is intentional or if it's just an unexamined consequence of the underlying control used for list view in the recent Cocoa Finder. Either way, thumbs up.

    Double-clicking on the dividing line between two column headers in list view will "right-size" that column. For most columns, this means expanding or shrinking to minimally fit the widest value in the column. Date headers will progressively shrink to point to less verbose date formats. Supposedly, this worked intermittently in Leopard as well. But whether Cocoa is bringing this feature for the first time or is just making it labor correctly for the first time, it's a change for the better.

    Searching using the Finder's browser view is greatly improved by the implementation of one of those slight things that many users gain been clamoring for year after year. There's now a preference to select the default scope of the search field in the Finder window toolbar. Can I obtain an amen?

    Default Finder search location: configurable at last.Default Finder search location: configurable at last.

    Along similar lines, there are other long-desired enhancements that will Go a long pass towards making the desktop environment feel more solid. A superior instance is the improved handling of the dreaded "cannot eject, disk in use" error. The obvious follow-up question from the user is, "Okay, so what's using it?" Snow Leopard finally provides that information.

    No more guessingNo more guessing

    (Yes, Mac OS X will rebuff to oust a disk if your current working directory in a command-line shell is on that disk. kindly of cool, but besides kindly of annoying.)

    Another feasible user response to a disk-in-use mistake is, "I don't care. I'm in a hurry. Just oust it!" That's an option now as well.

    Forcible ejection in progressForcible ejection in progress

    Hm, but why did I obtain information about the offending application in one dialog, an option to accommodate ejection in the other, but neither one presented both choices? It's a mystery to me, but presumably it's related to exactly what information the Finder has about the contention for the disk. (As always, the lsof command is available if you want to design it out the old-fashioned way.)

    Ummm…Ummm…

    So does the recent Cocoa Finder finally banish whole of those embarrassing bugs from the bad-old days of Carbon? Not quite. This is essentially the "1.0" release of the Cocoa Finder, and it has its share of 1.0 bugs. Here's one discovered by Glen Aspeslagh (see image right).

    Do you perceive it? If not, stare closer at the order of the dates in the supposedly sorted "Date Modified" column. So yeah, that ancient Finder magic has not been entirely extinguished.

    There besides remains some weirdness in the operation of the icon grid. In a view where grid snap is turned on (or is enabled transiently by holding down the command key during a drag) icons seem terrified of each other, leaving huge distances between themselves and their neighbors when they select which grid spot to snap to. It's as if the Finder lives in mortal terror that one of these files will someday obtain a 200-character filename that will overlap with a neighboring file's name.

    The worst incarnation of this conduct happens along the privilege edge of the screen where mounted volumes exhibit on the desktop. (Incidentally, this is not the default; if you want to perceive disks on your desktop, you must enable this preference in the Finder.) When I mount a recent disk, I'm often surprised to perceive where it ends up appearing. If there are any icons remotely immediate to the privilege edge of the screen, the disk icon will rebuff to exhibit there. Again, the Finder is not avoiding any actual designation or icon overlapping. It appears to exist avoiding the mere possibility of overlapping at some unspecified point in the future. Silly.

    Finder report card

    Overall, the Snow Leopard Finder takes several significant steps forward—64-bit/Cocoa future-proofing, a few new, useful features, added polish—and only a few shuffles backwards with the slight overuse of animation and the continued presence of some puzzling bugs. Considering how long it took the Carbon Finder to obtain to its pre-Snow-Leopard feature set and flat of polish, it's quite an achievement for a Cocoa Finder to match or exceed its predecessor in its very first release. I'm certain the Carbon vs. Cocoa warriors would gain had a field day with that statement, were Carbon not attach out to pasture in Leopard. But it was, and to the victor Go the spoils.

    Exchange

    Snow Leopard's headline "one recent feature" is advocate for Microsoft Exchange. This appears to be, at least partially, yet another hand-me-down from the iPhone, which gained advocate for Exchange in its 2.0 release and expanded on it in 3.0. Snow Leopard's Exchange advocate is weaved throughout the expected crop of applications in Mac OS X: iCal, Mail, and Address Book.

    The mountainous caveat is that it will only labor with a server running Exchange 2007 (Service Pack 1, Update Rollup 4) or later. While I'm certain Microsoft greatly appreciates any additional upgrade revenue this determination provides, it means that for users whose workplaces are soundless running older versions of Exchange, Snow Leopard's "Exchange support" might as well not exist.

    Those users are probably already running the only other viable Mac OS X Exchange client, Microsoft Entourage, so they'll likely just sit tense and wait for their IT departments to upgrade. Meanwhile, Microsoft is already making overtures to these users with the promised creation—finally—of an honest-to-goodness version of Outlook for Mac OS X.

    In my admittedly brief testing, Snow Leopard's Exchange advocate seems to labor as expected. I had to gain one of the Microsoft mavens in the Ars Orbiting HQ spin up an Exchange 2007 server just for the purposes of this review. However it was configured, whole I had to enter in the Mail application was my full name, e-mail address, and password, and it automatically discovered whole material settings and configured iCal and Address reserve for me.

    Exchange setup: surprisingly easyExchange setup: surprisingly easy

    Windows users are no doubt accustomed to this kindly of Exchange integration, but it's the first time I've seen it on the Mac platform—and that includes my many years of using Entourage.

    Access to Exchange-related features is decidedly subdued, in keeping with the existing interfaces for Mail, iCal, and Address Book. If you're expecting the swarm of panels and toolbar buttons organize in Outlook on Windows, you're in for a bit of a shock. For example, here's the "detail" view of a meeting in iCal.

    iCal event detailiCal event detail

    Clicking the "edit" button hardly reveals more.

    Event editor: that's it?Event editor: that's it?

    The "availability" window besides includes the bare minimum number of controls and displays to obtain the job done.

    Meeting availability checker Enlarge / Meeting availability checker

    The integration into Mail and Address reserve is even more subtle—almost entirely transparent. This is to exist construed as a feature, I suppose. But though I don't know enough about Exchange to exist completely sure, I can't shiver the passion that there are Exchange features that remain inaccessible from Mac OS X clients. For example, how effect I reserve a "resource" in a meeting? If there's a pass to effect so, I couldn't learn it.

    Still, even basic Exchange integration out-of-the-box goes long pass towards making Mac OS X more welcome in corporate environments. It remains to exist seen how convinced IT managers are of the "realness" of Snow Leopard's Exchange integration. But I've got to reason that being able to transmit and receive mail, create and respond to meeting invitations, and exercise the global corporate address reserve is enough for any Mac user to obtain along reasonably well in an Exchange-centric environment.

    Performance

    The thing is, there's not really much to Tell about performance in Snow Leopard. Dozens of benchmark graphs lead to the identical simple conclusion: Snow Leopard is faster than Leopard. Not shockingly so, at least in the aggregate, but it's faster. And while isolating one particular subsystem with a micro-benchmark may divulge some impressive numbers, it's the pass these wee changes combine to better the real-world undergo of using the system that really makes a difference.

    One instance Apple gave at WWDC was making an initial Time Machine backup over the network to a Time Capsule. Apple's approach to optimizing this operation was to address each and every subsystem involved.

    Time Machine itself was given advocate for overlapping i/o. Spotlight indexing, which happens on Time Machine volumes as well, was identified as another time-consuming task involved in backups, so its performance was improved. The networking code was enhanced to consume handicap of hardware-accelerated checksums where possible, and the software checksum code was hand-tuned for maximum performance. The performance of HFS+ journaling, which accompanies each file system metadata update, was besides improved. For Time Machine backups that write to disk images rather than indigenous HFS+ file systems, Apple added advocate for concurrent access to disk images. The amount of network traffic produced by AFP during backups has besides been reduced.

    All of this adds up to a respectable 55% overall improvement in the speed of an initial Time Machine backup. And, of course, the performance improvements to the individual subsystems capitalize whole applications that exercise them, not just Time Machine.

    This holistic approach to performance improvement is not likely to knock anyone's socks off, but every time you rush across a piece of functionality in Snow Leopard that disproportionately benefits from one of these optimized subsystems, it's a pleasure.

    For example, Snow Leopard shuts down and restarts much faster than Leopard. I'm not talking about boot time; I exist necessary the time between the selection of the Shutdown or Restart command and when the system turns off or begins its recent boot cycle. Leopard doesn't consume long at whole to effect this; only a few dozen of seconds when there are no applications open. But in Snow Leopard, it's so hasty that I often thought the operating system had crashed rather than shut down cleanly. (That's actually not too far from the truth.)

    The performance boosts offered by earlier major releases of Mac OS X soundless dwarf Snow Leopard's speedup, but that's mostly because Mac OS X was so excruciatingly sluggish in its early years. It's smooth to create a mountainous performance delta when you're starting from something abysmally slow. The fact that Snow Leopard achieves consistent, measurable improvements over the already-speedy Leopard is whole the more impressive.

    And yes, for the seventh consecutive time, a recent release of Mac OS X is faster on the identical hardware than its predecessor. (And for the first time ever, it's smaller, too.) What more can you quest information from for, really? Even that ancient performance bugaboo, window resizing, has been completely vanquished. Grab the corner of a fully-populated iCal window—the worst-case scenario for window resizing in the ancient days—and shiver it as hasty as you can. Your cursor will never exist more than a few millimeters from the window's grab handle; it tracks your frantic motion perfectly. On most Macs, this is actually staunch in Leopard as well. It just goes to point to how far Mac OS X has approach on the performance front. These days, they whole just consume it for granted, which is exactly the pass it should be.

    Grab bag

    In the "grab bag" section, I usually examine smaller, mostly unrelated features that don't warrant full-blown sections of their own. But when it comes to user-visible features, Snow Leopard is kindly of "all grab bag," if you know what I mean. Apple's even got its own incarnation in the form of a giant webpage of "refinements." I'll probably overlap with some of those, but there'll exist a few recent ones here as well.

    New columns in open/save dialogs

    The list view in open and deliver dialog boxed now supports more than just "Name" and "Date Modified" columns. Right-click on any column to obtain a preference of additional columns to display. I've wanted this feature for a long time, and I'm glad someone finally had time to implement it.

    Configurable columns in open/save dialogsConfigurable columns in open/save dialogs Improved scanner support

    The bundled Image Capture application now has the faculty to talk to a wide ambit of scanners. I plugged in my Epson Stylus CX7800, a device that previously required the exercise of third-party software in order to exercise the scanning feature, and Image Capture detected it immediately.

    Epson scanner + Image Capture - Epson software Enlarge / Epson scanner + Image Capture - Epson software

    Image Capture is besides not a evil slight scanning application. It has pretty superior automatic remonstrate detection, including advocate for multiple objects, obviating the need to manually crop items. Given the sometimes-questionable character of third-party printer and scanner drivers for Mac OS X, the faculty to exercise a bundled application is welcome.

    System Preferences bit wars

    System Preferences, like virtually whole other applications in Snow Leopard, is 64-bit. But since 64-bit applications can't load 32-bit plug-ins, that presents a problem for the existing crop of 32-bit third-party preference panes. System Preferences handles this situation with a reasonable amount of grace. On launch, it will panoply icons for whole installed preference panes, 64-bit or 32-bit. But if you click on a 32-bit preference pane, you'll exist presented with a notification like this:

    64-bit application vs. 32-bit plug-in: fight!64-bit application vs. 32-bit plug-in: fight!

    Click "OK" and System Preferences will relaunch in 32-bit mode, which is conveniently indicated in the title bar. Since whole of the first-party preference panes are compiled for both 64-bit and 32-bit operation, System Preferences does not need to relaunch again for the duration of its use. This raises the question, why not gain System Preferences launch in 32-bit mode whole the time? I suspect it's just another pass for Apple to "encourage" developers to build 64-bit-compatible binaries.

    Safari plug-ins

    The inability of of 64-bit applications load 32-bit plug-ins is a problem for Safari as well. Plug-ins are so necessary to the Web undergo that relaunching in 32-bit mode is not really an option. You'd probably need to relaunch as soon as you visited your first webpage. But Apple does want Safari to rush in 64-bit mode due to some significant performance enhancements in the JavaScript engine and other areas of the application that are not available in 32-bit mode.

    Apple's solution is similar to what it did with QuickTime X and 32-bit QuickTime 7 plug-ins. Safari will rush 32-bit plug-ins in divide 32-bit processes as needed.

    Separate processes for 32-bit Safari plug-insSeparate processes for 32-bit Safari plug-ins

    This has the added, extremely significant capitalize of isolating potentially buggy plug-ins. According to the automated crash reporting built into Mac OS X, Apple has said that the number one occasions of crashes is Web browser plug-ins. That's not the number one occasions of crashes in Safari, intuition you, it's the number one occasions when considering whole crashes of whole applications in Mac OS X. (And though it was not mentioned by name, I reason they whole know the primary culprit.)

    As you can perceive above, the QuickTime browser plug-in gets the identical treatment as twinkle and other third-party 32-bit Safari plug-ins. whole of this means that when a plug-in crashes, Safari in Snow Leopard does not. The window or tab containing the crashing plug-in doesn't even close. You can simply click the reload button and give the problematic plug-in another random to duty correctly.

    While this is soundless far from the much more robust approach employed by Google Chrome, where each tab lives in its own independent process, if Apple's crash statistics are to exist believed, isolating plug-ins may generate most of the capitalize of truly divide processes with a significantly less radical change to the Safari application itself.

    Resolution independence

    When they ultimate left Mac OS X in its seemingly interminable march towards a truly scalable user interface, it was almost ready for prime time. I'm desolate to Tell that resolution independence was obviously not a priority in Snow Leopard, because it hasn't gotten any better, and may gain actually regressed a bit. Here's what TextEdit looks like at a 2.0 scale factor in Leopard and Snow Leopard.

    TextEdit at scale factor 2.0 in LeopardTextEdit at scale factor 2.0 in Leopard TextEdit at scale factor 2.0 in Snow LeopardTextEdit at scale factor 2.0 in Snow Leopard

    Yep, it's a bummer. I soundless bethink Apple advising developers to gain their applications ready for resolution independence by 2008. That's one of the few dates that the Jobs-II-era Apple has not been able to hit, and it's getting later whole the time. On the other hand, it's not like 200-DPI monitors are raining from the sky either. But I'd really like to perceive Apple obtain going on this. It will undoubtedly consume a long time for everything to stare and labor correctly, so let's obtain started.

    Terminal splitters

    The Terminal application in Tiger and earlier versions of Mac OS X allowed each of its windows to exist split horizontally into two divide panes. This was invaluable for referencing some earlier text in the scrollback while besides typing commands at the prompt. Sadly, the splitter feature disappeared in Leopard. In Snow Leopard, it's back with a vengeance.

    Arbitrary splitters, baby!Arbitrary splitters, baby!

    (Now if only my favorite text editor would obtain on board the train to splittersville.)

    Terminal in Snow Leopard besides defaults to the recent Menlo font. But wayward to earlier reports, the One staunch Monospaced Font, Monaco, is most definitely soundless included in Snow Leopard (see screenshot above) and it works just fine.

    System Preferences shuffle

    The seemingly obligatory rearrangement of preference panes in the System Preferences application accompanying each release of Mac OS X continues in Snow Leopard.

    System Preferences: shuffled yet again Enlarge / System Preferences: shuffled yet again System Preferences (not running) with Dock menuSystem Preferences (not running) with Dock menu

    This time, the "Keyboard & Mouse" preference pane is split into divide "Keyboard" and "Mouse" panes, "International" becomes "Language & Text," and the "Internet & Network" section becomes "Internet & Wireless" and adopts the Bluetooth preference pane.

    Someday in the faraway future, perhaps Apple will finally arrive at the "ultimate" arrangement of preference panes and they can whole finally Go more than two years without their muscle recollection being disrupted.

    Before stirring on, System Preferences has one super trick. You can launch directly into a specific preference pane by right-clicking on System Preferences's Dock icon. This works even when System Preferences is not yet running. kindly of creepy, but useful.

    Core location

    One more gift from the iPhone, Core Location, allows Macs to design out where in the world they are. The "Date & Time" preference pane offers to set your time zone automatically based on your current location using this newfound ability.

    Set your Mac's time zone automatically based on your current location, thanks to Core Location.Set your Mac's time zone automatically based on your current location, thanks to Core Location. Keyboard magic

    Snow Leopard includes a simple facility for system-wide text auto-correction and expansion, accessible from the "Language & Text" preference pane. It's not quite ready to give a dedicated third-party application a rush for its money, but hey, it's free.

    Global text expansion and auto-correction Enlarge / Global text expansion and auto-correction

    The keyboard shortcuts preference pane has besides been rearranged. Now, instead of a single, long list of system-wide keyboard shortcuts, they're arranged into categories. This reduces clutter, but it besides makes it a bit more difficult to find the shortcut you're interested in.

    Keyboard shortcuts: now with categories Enlarge / Keyboard shortcuts: now with categories The sleeping Mac dilemma

    I don't like to leave my Mac Pro turned on 24 hours a day, especially during the summer in my un-air-conditioned house. But I effect want to gain access to the files on my Mac when I'm elsewhere—at work, on the road, etc. It is feasible to wake a sleeping Mac remotely, but doing so requires being on the identical local network.

    My solution has been to leave a smaller, more power-efficient laptop on at whole times on the identical network as my Mac Pro. To wake my Mac Pro remotely, I ssh into the laptop, then transmit the magic "wake up" packet to my Mac Pro. (For this to work, the "Wake for Ethernet network administrator access" checkbox must exist checked in the "Energy Saver" preference pane in System Preferences.)

    Snow Leopard provides a pass to effect this without leaving any of my computers running whole day. When a Mac running Snow Leopard is attach to sleep, it attempts to hand off ownership of its IP address to its router. (This only works with an AirPort Extreme basis station from 2007 or later, or a Time Capsule from 2008 or later with the latest (7.4.2) firmware installed.) The router then listens for any attempt to connect to the IP address. When one occurs, it wakes up the original owner, hands back the IP address, and forwards traffic appropriately.

    You can even wake some recent-model Macs over WiFi. Combined with MobileMe's "Back to My Mac" dynamic DNS thingamabob, it means I can leave whole my Macs asleep and soundless gain access to their contents anytime, anywhere.

    Back to my hack

    As has become traditional, this recent release of Mac OS X makes life a bit harder for developers whose software works by patching the in-memory representation of other running applications or the operating system itself. This includes Input Managers, SIMBL plug-ins, and of course the dreaded "Haxies."

    Input Managers obtain the worst of it. They've actually been unsupported and non-functional in 64-bit applications since Leopard. That wasn't such a mountainous deal when Mac OS X shipped with a whopping two 64-bit applications. But now, with almost every application in Snow Leopard going 64-bit, it's suddenly very significant.

    Thanks to Safari's lack of an officially sanctioned extension mechanism, developers looking to enhance its functionality gain most often resorted to the exercise of Input Managers and SIMBL (which is an Input-Manager-based framework). A 64-bit Safari puts a damper on that entire market. Though it is feasible to manually set Safari to launch in 32-bit mode—Get Info on the application in the Finder and click a checkbox—ideally, this is not something developers want to accommodate users to do.

    Happily, at least one commonly used Safari enhancement has the superior fortune to exist built on top of the officially supported browser plug-in API used by Flash, QuickTime, etc. But that may not exist a feasible approach for Safari extensions that enhance functionality in ways not tied directly to the panoply of particular types of content within a webpage.

    Though I blueprint to rush Safari in its default 64-bit mode, I'll really miss Saft, a Safari extension I exercise for session restoration (yes, I know Safari has this feature, but it's activated manually—the horror) and address bar shortcuts (e.g., "w noodles" to stare up "noodles" in Wikipedia). I'm hoping that clever developers will find a pass to overcome this recent challenge. They always seem to, in the end. (Or Apple could add a proper extension system to Safari, of course. But I'm not holding my breath.)

    As for the Haxies, those usually crash with each major operating system update as a matter of course. And each time, those determined fellows at Unsanity, against whole odds, manage to preserve their software working. I salute them for their effort. I delayed upgrading to Leopard for a long time based solely on the absence of my beloved WindowShade X. I hope I don't gain to wait too long for a Snow-Leopard-compatible version.

    The general trend in Mac OS X is away from any sort of involuntary recollection space sharing, and towards "external" plug-ins that live in their own, divide processes. Even contextual menu plug-ins in the Finder gain been disabled, replaced by an enhanced, but soundless less-powerful Services API. Again, I gain faith that developers will adapt. But the waiting is the hardest part.

    ZFS MIA

    It looks like we'll whole exist waiting a while longer for a file system in shining armor to supersede the venerable HFS+ (11 years young!) as the default file system in Mac OS X. Despite rumors, outright declarations, and much actual pre-release code, advocate for the impressive ZFS file system is not present in Snow Leopard.

    That's a shame because Time Machine veritably cries out for some ZFS magic. What's more, Apple seems to agree, as evidenced by a post from an Apple employee to a ZFS mailing list ultimate year. When asked about a ZFS-savvy implementation of Time Machine, the reply was encouraging: "This one is necessary and likely will approach sometime, but not for SL." ("SL" is short for Snow Leopard.)

    There are many reasons why ZFS (or a file system with similar features) is a flawless fit for Time Machine, but the most necessary is its faculty to transmit only the block-level changes during each backup. As Time Machine is currently implemented, if you construct a wee change to a giant file, the entire giant file is copied to the Time Machine volume during the next backup. This is extremely wasteful and time consuming, especially for large files that are modified constantly during the day (e.g., Entourage's e-mail database). Time Machine running on top of ZFS could transfer just the changed disk blocks (a maximum of 128KB each in ZFS, and usually much smaller).

    ZFS would besides bring vastly increased robustness for data and metadata, a pooled storage model, constant-time snapshots and clones, and a pony. People sometimes quest information from what, exactly, is wrong with HFS+. Aside from its obvious lack of the features just listed, HFS+ is limited in many ways by its dated design, which is based on HFS, a twenty-five year-old file system.

    To give just one example, the centrally located Catalog File, which must exist updated for each change to the file system's structure, is a frequent and inevitable source of contention. Modern file systems usually spread their metadata around, both for robustness (multiple copies are often kept in divide locations on the disk) and to allow for better concurrency.

    Practically speaking, reason about those times when you rush Disk Utility on an HFS+ volume and it finds (and hopefully repairs) a bunch of errors. That's bad, okay? That's something that should not befall with a modern, thoroughly checksummed, always-consistent-on-disk file system unless there are hardware problems (and a ZFS storage pool can actually deal with that as well). And yet it happens whole the time with HFS+ disks in Mac OS X when various bits of metadata obtain corrupted or become out of date.

    Apple gets by year after year, tacking recent features onto HFS+ with duct tape and a prayer, but at a certain point there simply has to exist a successor—whether it's ZFS, a home-grown Apple file system, or something else entirely. My fingers are crossed for Mac OS X 10.7.

    The future soon

    Creating an operating system is as much a companionable exercise as a technological one. Creating a platform, even more so. whole of Snow Leopard's considerable technical achievements are not just designed to capitalize users; they're besides intended to goad, persuade, and otherwise herd developers in the direction that Apple feels will exist most profitable for the future of the platform.

    For this to work, Snow Leopard has to actually find its pass into the hands of customers. The pricing helps a lot there. But even if Snow Leopard were free, there's soundless some cost to the consumer—in time, worry, software updates, etc.—when performing a major operating system upgrade. The identical goes for developers who must, at the very least, certify that their existing applications rush correctly on the recent OS.

    The accustomed pass to overcome this kindly of upgrade hesitation has been to pack the OS with recent features. recent features sell, and the more copies of the recent operating system in use, the more motivated developers are to update their applications to not just rush on the recent OS, but besides consume handicap of its recent abilities.

    A major operating system upgrade with "no recent features" must play by a different set of rules. Every party involved expects some counterbalance to the lack of recent features. In Snow Leopard, developers stand to gleam the biggest benefits thanks to an impressive set of recent technologies, many of which cover areas previously unaddressed in Mac OS X. Apple clearly feels that the future of the platform depends on much better utilization of computing resources, and is doing everything it can to construct it smooth for developers to coast in this direction.

    Though it's obvious that Snow Leopard includes fewer external features than its predecessor, I'd wager that it has just as many, if not more internal changes than Leopard. This, I fear, means that the initial release of Snow Leopard will likely suffer the typical 10.x.0 bugs. There gain already been reports of recent bugs introduced to existing APIs in Snow Leopard. This is the exact contrary of Snow Leopard's implied pledge to users and developers that it would concentrate on making existing features faster and more robust without introducing recent functionality and the accompanying recent bugs.

    On the other side of the coin, I imagine whole the teams at Apple that worked on Snow Leopard absolutely reveled in the break to polish their particular subsystems without being burdened by supporting the marketing-driven feature-of-the-month. In any long-lived software product, there needs to exist this kindly of release valve every few years, lest the entire code basis Go off into the weeds.

    There's been one other "no recent features" release of Mac OS X. Mac OS X 10.1, released a mere six months after version 10.0, was handed out for free by Apple at the 2001 Seybold publishing conference and, later, at Apple retail stores. It was besides available from Apple's online store for $19.95 (along with a copy of Mac OS 9.2.1 for exercise in the Classic environment). This was a different time for Mac OS X. Versions 10.0 and 10.1 were slow, incomplete, and extremely immature; the transition from classic Mac OS was far from over.

    Judged as a modern incarnation of the 10.1 release, Snow Leopard looks pretty darned good. The pricing is similar, and the benefits—to developers and to users—are greater. So is the risk. But again, that has more to effect with how horrible Mac OS X 10.0 was. Choosing not to upgrade to 10.1 was unthinkable. Waiting a while to upgrade to Snow Leopard is reasonable if you want to exist certain that whole the software you custody about is compatible. But don't wait too long, because at $29 for the upgrade, I anticipate Snow Leopard adoption to exist quite rapid. Software that will rush only on Snow Leopard may exist here before you know it.

    Should you buy Mac OS X Snow Leopard? If you're already running Leopard, then the respond is a resounding "yes." If you're soundless running Tiger, well, then it's probably time for a recent Mac anyway. When you buy one, it'll approach with Snow Leopard.

    As for the future, it's tempting to view Snow Leopard as the "tick" in a recent Intel-style "tick-tock" release strategy for Mac OS X: radical recent features in version 10.7 followed by more Snow-Leopard-style refinements in 10.8, and so on, alternating between "feature" and "refinement" releases. Apple has not even hinted that they're considering this character of plan, but I reason there's a lot to recommend it.

    Snow Leopard is a unique and glowing release, unlike any that gain approach before it in both scope and intention. At some point, Mac OS X will surely need to obtain back on the bullet-point-features bandwagon. But for now, I'm content with Snow Leopard. It's the Mac OS X I know and love, but with more of the things that construct it fragile and bizarre engineered away.

    Snowy eyes Looking back

    This is the tenth review of a full Mac OS X release, public beta, or developer preview to rush on Ars, dating back to December 1999 and Mac OS X DP2. If you want to jump into the Wayback Machine and perceive how far Apple has approach with Snow Leopard (or just want to bone up on whole of the mountainous cat monikers), we've gone through the archives and dug up some of their older Mac OS X articles. glad reading!

  • Five years of Mac OS X, March 24, 2006
  • Mac OS X 10.5 Leopard, October 28, 2007
  • Mac OS X 10.4 Tiger, April 28, 2005
  • Mac OS X 10.3 Panther, November 9, 2003
  • Mac OS X 10.2 Jaguar, September 5, 2002
  • Mac OS X 10.1 (Puma), October 15, 2001
  • Mac OS X 10.0 (Cheetah), April 2, 2001
  • Mac OS X Public Beta, October 3, 2000
  • Mac OS X Q & A, June 20, 2000
  • Mac OS X DP4, May 24, 2000
  • Mac OS X DP3: ordeal by Water, February 28, 2000
  • Mac OS X Update: Quartz & Aqua, January 17, 2000
  • Mac OS X DP2, December 14, 1999

  • Discovering Mac OS X 10.6 Snow Leopard | killexams.com real questions and Pass4sure dumps

    See what Apple gives you in this Mac OS X update for just $29. You won't perceive mountainous interface changes, but there has been a lot of labor done under the hood. Eric Geier discusses most of the performance enhancements and recent features.

    Like this article? They recommend 

    Apple released an update to the Mac OS X operating system (OS), Snow Leopard, at the immediate of August. This makes it version 10.6. Although it might not gain as many visual changes as Windows 7 does from Vista, it does gain many notable enhancements and additions. The first thing you'll probably notice is the price: It's only $29 to upgrade from version 10.5.

    Since Tiger, Apple has been adding more and more 64-bit support. The Mac OS X kernel in Snow Leopard and most of the OS applications gain been rebuilt to rush at 64-bit in addition to 32-bit. However, this excludes iTunes, Front Row, Grapher, and DVD Player applications. Plus privilege now only a select number of Apple computers are compatible with whole the added support.

    If you aren't a power user and gain a typical 32-bit processor, this doesn't abet you out. But if you effect invest in a more powerful system, Mac OS X is ready more than ever.

    Running a 64-bit processor means it can process bigger chunks of data more quickly, giving you a faster, higher-performing computer.


    Mozilla to immediate Firefox advocate for OS X 10.6, 10.7, and 10.8 in August | killexams.com real questions and Pass4sure dumps

    Yesterday, Mozilla announced the immediate of Firefox advocate for Apple customers using Mac OS X versions 10.6, 10.7, and 10.8. The cutoff date is August 2016.

    Mozilla says it took this step following Apple's determination to immediate advocate for these OS X versions as well.

    Apple released Mac OS X 10.6 (Snow Leopard) in August 2009, Mac OS X 10.7 (Lion) in July 2011, and Mac OS X 10.8 (Mountain Lion) in July 2012. Apple announced the immediate of official advocate for Snow Leopard in February 2014, for Lion in October 2014, and for Mountain Lion in December 2014.

    Now, Mozilla is proverb that, after August 2016, Firefox versions running on these operating systems will no longer receive recent features or security updates.

    Firefox ESR (Extended advocate Release) will continue to advocate these three OS versions until mid-August 2017, when it will besides desist delivering recent features or security updates.

    At the start of the month, Google besides pulled the plug on Google Chrome for OS X 10.6, 10.7, and 10.8, along with Windows XP and Vista.

    According to statistics at the immediate of October 2015, not a soul of the aforementioned OS X versions had a market share above 10% among Mac users. The biggest chunk belonged to Snow Leopard, but most Mac users already started migrating to Mavericks (10.9), Yosemite (10.10) and El Capitan (10.11).

    "Mozilla strongly encourages their users to upgrade to a version of OS X currently supported by Apple. Unsupported operating systems receive no security updates, gain known exploits, and are perilous for you to use," Mozilla advised customers yesterday.



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