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9L0-060 Mac OS X 10.4 Service and Support

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9L0-060 exam Dumps Source : Mac OS X 10.4 Service and Support

Test Code : 9L0-060
Test designation : Mac OS X 10.4 Service and Support
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: 50 real Questions

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Mac OS X 10.4 Service and Support

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Watch: Mac OS X 10.4 Running in Windows Alternative ReactOS via PearPC Emulator | killexams.com real questions and Pass4sure dumps

The ReactOS project recently showcased on YouTube that's possible to virtualize the Mac OS X 10.4 operating system on their free and open-source Windows alternative operating system.

Our "Watch" string of articles continues today with a very provocative one where you can note Mac OS X 10.4 Tiger running inside the ReactOS computer operating system, which they believe has near a long way, and it's birth to eye enjoy a viable alternative to Microsoft's Windows 7 or Vista operating systems, impeccable for desktop computers and laptops.

The latest release, ReactOS 0.4.8, showed us ultimate month that it's now possible to employ Windows 10, Windows 8, and Windows Vista software on the free and open-source operating system that's binary compatible with computer programs and device drivers made for Windows.

It besides introduced initial support for reading data from NTFS formatted drives, a modern app similar to the DrWatson32 software for Windows, some user-visible changes enjoy support for balloon notifications in the system tray zone and support for unmounting network drives directly from the file explorer.

You can now emulate various operating systems inside ReactOS

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Why would you flee an older version of Mac OS X inside ReactOS? Well, that doesn't really matter, but what's indispensable here is that you can employ the PearPC emulator to virtualize various other PowerPC operating systems, including Mac OS X, Darwin, and GNU/Linux, which is both educational and entertaining. Check it out in action below!

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 with 269 posters participating, including Story author Share this story
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  • Mac OS X 10.4 Tiger: 150+  modern featuresMac OS X 10.4 Tiger: 150+ modern 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 drive reflected this, touting "over 150 modern features."

    All those modern 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 goal to jog 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  modern features in Mac OS X 10.5 LeopardSteve Jobs at WWDC 2007, touting 300 modern features in Mac OS X 10.5 Leopard

    Apple even went so far as to list bar no one at all 300 modern features on its website. As it turns out, "spring" was a bit optimistic. Leopard actually shipped at the conclude of October 2007, nearly two and a half years after Tiger. Did Leopard really beget twice as many modern features as Tiger? That's debatable. What's sure is that Leopard included a solid crop of modern features and technologies, many of which they now capture for granted. (For example, beget 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 live maturing. The progression was clear: longer release cycles, more features. What would Mac OS X 10.6 live like? Would it arrive three and a half years after Leopard? Would it and comprise 500 modern features? A thousand?

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

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

    That's right, the next major release of Mac OS X would beget no modern features. The product designation reflected this: "Snow Leopard." Mac OS X 10.6 would merely live 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 modern features and APIs in 10.4 and 10.5, could Apple really rate 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? involuntary applause. There were even a few hoots and whistles.

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

    It probably helps to know that the "0 modern Features" slip came at the conclude of an hour-long presentation detailing the major modern APIs and technologies in Snow Leopard. It was besides quickly followed by a back-pedaling ("well, there is one modern feature...") slip describing the addition of Microsoft Exchange support. In isolation, "no modern 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 enjoy this: "We're adding a ton of modern things to Mac OS X that will serve you write better applications and get your existing code flee faster, and we're going to get sure that bar no one at all this modern stuff is rock-solid and as bug-free as possible. We're not going to overextend ourselves adding a raft of modern customer-facing, marketing-friendly features. Instead, we're going to concentrate 100% on the things that impress you, the developers."

    But if Snow Leopard is a treasure epistle to developers, is it a Dear John epistle to users? You know, those people that the marketing department might so crudely advert 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 support up with Apple's seemingly never-ending stream of modern APIs, it can live just as taxing for customers to sojourn on top of Mac OS X's features. Exposé, a modern Finder, Spotlight, a modern Dock, Time Machine, a modern Finder again, a modern iLife and iWork almost every year, and on and on. And as much as developers dislike bugs in Apple's APIs, users who suffer those bugs as application crashes beget just as much intuition to live annoyed.

    Enter Snow Leopard: the release where they bar no one at all rate a shatter 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 modern APIs and technologies?" When speaking to developers, Apple's message of "no modern features" is another passage of maxim "no modern bugs." Snow Leopard is hypothetical to fix traditional bugs without introducing modern ones. But nothing says "new bugs, coming right up" quite enjoy major modern APIs. So which is it?

    Similarly, for users, "no modern 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 get honorable on this promise? Or will users conclude up with bar no one at all the disadvantages of a feature-packed release enjoy Tiger or Leopard—the inevitable 10.x.0 bugs, the unfamiliar, untried modern functionality—but without any of the actual modern features?

    Yes, it's enough to get one quite cynical about Apple's real motivations. To fling some more fuel on the fire, beget a eye 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 modern features. (The releases are distributed uniformly on the Y axis.) Maybe you consider it's reasonable for the time between releases to stretch out as each one brings a heavier load of goodies than the last, but support in intuition the analytic consequence of such a curve over the longhorn haul.

    And yeah, there's a slight upwards kick at the conclude for 10.6, but remember, this is hypothetical to live the "no modern 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 arduous not to sensation 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, noiseless in that steep, early section of its own timeline graph. Yes, I'm talking about the iPhone, specifically iPhone OS. The iPhone business has exploded onto Apple's equipoise sheets enjoy 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 beget been reassigned to iPhone OS (temporarily or otherwise). After all, Mac OS X and iPhone OS share the very core operating system, the very language for GUI development, and many of the very 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 live announced for the Mac first (because the iPhone was noiseless a secret), enjoy Core Animation and code signing. Such machination theories certainly aren't helped by WWDC keynote snubs and other indignities suffered by Mac OS X and the Mac in common 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 bar no one at all that? A nearly two-year evolution cycle, but no modern features. Major modern frameworks for developers, but few modern bugs. Significant changes to the core OS, but more reliability. And a franchise rejuvenation with few user-visible changes.

    It's enough to swirl 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 beget bar no one at all been $129, with no special pricing for upgrades. After eight years of this kindhearted of fiscal disciplining, Leopard users may well live tempted to quit reading right now and just fade 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 smooth of faith in Apple's competence to help the OS with each release, and boom, instant purchase.

    Still here? Good, because there's something else you necessity 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 flee on Macs with Intel CPUs. Sorry (again), PowerPC fans, but this is the conclude of the line for you. The transition to Intel was announced over four years ago, and the ultimate modern 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 modern features" stance (and the accompanying necessity 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 serve shove them over the (likely) four-digit charge wall of a modern Mac. For PowerPC Mac owners, the threshold for a modern Mac purchase remains mostly unchanged. When their traditional Mac breaks or seems too slow, they'll fade out and buy a modern one, and it'll near with Snow Leopard pre-installed.

    If Snow Leopard does conclude up motivating modern Mac purchases by PowerPC owners, it will probably live 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 support on the Mac platform.

    The final provocative group is owners of Intel-based Macs that are noiseless 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 boom about Snow Leopard's pricing (emphasis added).

    Mac OS X version 10.6 Snow Leopard will live available as an upgrade to Mac OS X version 10.5 Leopard in September 2009 [...] The Snow Leopard lone user license will live available for a suggested retail charge of $29 (US) and the Snow Leopard Family Pack, a lone household, five-user license, will live 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 live 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 live free with your modern Mac, $29 if you're already running Leopard, or $169 if you beget an Intel Mac running Tiger. People upgrading from Tiger will rate the latest version of iLife and iWork in the covenant (if that's the confiscate term), whether they want them or not. It sure seems enjoy there's an obvious region in this lineup for a $129 offering of Snow Leopard on its own. Then again, perhaps it bar no one at all 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 outcome on your competence to flee the OS. This is considered a genuine edge of Mac OS X, but it besides means that Apple has no dependable 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 sort of thing before, and it bypasses any proof-of-purchase annoyances. It would, however, introduce a modern problem. In the event of a arduous drive failure or simple decision to reinstall from scratch, owners of the $29 Snow Leopard upgrade would live 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 beget 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 vacuous arduous drive.

    To live 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 decision is a refreshing change: rewarding honest people with a hassle-free product rather than trying to chastise mendacious people by treating everyone enjoy a criminal. This "honor system" upgrade enforcement policy partially explains the vast jump to $169 for the Mac Box Set, which ends up re-framed as an honest person's passage to rate iLife and iWork at their usual prices, plus Snow Leopard for $11 more.

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


    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 hasten of the optical drive, and so on. Installation besides only happens once, and it's not really an provocative process unless something goes terribly wrong. Still, if Apple's going to get such a claim, it's worth checking out.

    To liquidate as many variables as possible, I installed both Leopard and Snow Leopard from one arduous disk onto another (empty) one. It should live famed that this change negates some of Snow Leopard's most indispensable 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 note 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 tiny (5:49 vs. 3:20) and again, modern installations on vacuous disks are not the norm. But the shorter wait for Spotlight indexing is worth noting because it's the first indication most users will rate that Snow Leopard means business 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 flee on Intel Macs. Okay Apple, they rate 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 betide when bar no one at all 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 live 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 employ 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 very facility to download and install printer drivers on demand, saving another trip to the installer DVD. I hope this technique gains even wider employ 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; note 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 live equal to 109 (1,000,000,000) bytes, whereas the Leopard Finder—and, it should live noted, every version of the Finder before it—equates 1 GB to 230 (1,073,741,824) bytes. This has the outcome of making your arduous disk suddenly issue larger after installing Snow Leopard. For example, my "1 TB" arduous 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 beget guessed, arduous disk manufacturers employ the powers-of-ten system. It's bar no one at all quite a mess, really. Though I near down pretty firmly on the powers-of-two side of the fence, I can't guilt Apple too much for wanting to match up nicely with the long-established (but noiseless dumb, intuition you) arduous disk vendors' capacity measurement standard.

    Snow Leopard has several weight loss secrets. The first is obvious: no PowerPC support means no PowerPC code in executables. Recall the maximum possible 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 bar no one at all 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 beget 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 inform you is that the commands shown above were flee from a Leopard system looking at a Snow Leopard disk. In fact, bar no one at all compressed Snow Leopard files issue to hold zero bytes when viewed from a pre-Snow Leopard version of Mac OS X. (They eye and act perfectly modest when booted into Snow Leopard, of course.)

    So, where's the data? The slight "@" at the conclude 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 beget 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 bar no one at all 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 arduous links. In Tiger, extended attributes and access control lists were incorporated. In Leopard, HFS+ gained support for arduous links to directories. In Snow Leopard, HFS+ learns another modern trick: per-file compression.

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

    Even more information is revealed with the serve 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 sort = 4 (resource fork has compressed data) uncompressed size = 7500336 bytes

    And sure enough, as they saw, the resource fork does indeed hold the compressed data. Still, why the resource fork? It's bar no one at all share of Apple's usual, clever backward-compatibility gymnastics. A recent instance is the passage that arduous links to directories exhibit 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 get 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, pervert through modification—the unexpectedly compressed file contents, Apple has chosen to conceal the compressed data instead.

    And where can the complete contents of a potentially great file live hidden in such a passage that pre-Snow Leopard systems can noiseless 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 moving or duplicating files. In Leopard, even the lowly cp and rsync commands will attain the same. So while it may live a slight bit spooky to note bar no one at all those "empty" 0 KB files when looking at a Snow Leopard disk from a pre-Snow Leopard OS, the casual of data loss is small, even if you jog or copy one of the files.

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

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

    Here, the data is tiny enough to live 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 sort = 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 gauge PkgInfo file enjoy this one, those contents are the four-byte classic Mac OS sort 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 noiseless the very "fpmc..." preamble seen in bar no one at all the earlier examples of the com.apple.decmpfs attribute, but at the conclude of the value, the expected data appears as modest as day: sort code "APPL" (application) and creator code "emal" (for the Mail application—cute, as per classic Mac OS tradition).

    You may live wondering, if this is bar no one at all about data compression, how does storing eight uncompressed bytes plus a 17-byte preamble in an extended attribute rescue any disk space? The reply 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 shroud size (4 KB, by default). So those eight bytes will capture up a minimum of 4,096 bytes if stored in the traditional way. When allocating disk space for extended attributes, however, the allocation shroud 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 attribute 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 arduous disk search times and rotational delays are noiseless measured in milliseconds. In one millisecond, a 2 GHz CPU goes through two million cycles. And then, of course, there's noiseless the actual data transfer time to consider.

    Granted, several levels of caching throughout the OS and hardware travail mightily to conceal these delays. But those bits beget to near off the disk at some point to fill those caches. Compression means that fewer bits beget to live transferred. Given the almost comical glut of CPU resources on a modern multi-core Mac under modest use, the total time needed to transfer a compressed payload from the disk and employ the CPU to decompress its contents into remembrance will noiseless usually live far less than the time it'd capture to transfer the data in uncompressed form.

    That explains the potential performance benefits of transferring less data, but the employ of extended attributes to store file contents can actually get things faster, as well. It bar no one at all has to attain with data locality.

    If there's one thing that slows down a arduous disk more than transferring a great amount of data, it's moving its heads from one share of the disk to another. Every jog 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 rescue the desired bits beneath it. These are bar no one at all real, physical, moving parts, and it's extraordinary that they attain their dance as quickly and efficiently as they do, but physics has its limits. These motions are the real performance killers for rotational storage enjoy arduous disks.

    The HFS+ volume format stores bar no one at all 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 live very great (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 circumscribe of about 128 bytes per attribute. But it besides means that the disk head doesn't necessity to capture a trip to another share of the disk to rate the actual data.

    As you can imagine, the disk blocks that get up the Catalog and Attributes files are frequently accessed, and therefore more likely than most to live in a cache somewhere. bar no one at all of this conspires to get 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 noiseless less than the allocation shroud size for modest data storage, and as long as it bar no one at all 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 provocative promises about the installation process:

    Snow Leopard checks your applications to get sure they're compatible and sets aside any programs known to live 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 boom "illicit"—third-party system extensions. I beget a decidedly pragmatic view of such software, and I'm cheerful to note Apple taking a similarly practical approach to minimizing its repercussion on users.

    Apple can't live expected to detect and disable bar no one at all potentially incompatible software, of course. I suspect only the most common or highest profile risky software is detected. If you're a developer, this installer feature may live a honorable passage to find out if you're on Apple's sh*t list.

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

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

    Snow Leopard's modern looks

    I've long yearned for Apple to get a clean break, at least visually, from Mac OS X's Aqua past. Alas, I will live 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 witness otherwise. The truth is, Snow Leopard actually changes the appearance of nearly every pixel on your screen—but not in the passage 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 leisure of the world—has used a value of 2.2. Though this may not seem significant to anyone but professional graphics artists, the inequity is usually clear-cut to even a casual observer when viewing the very 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 inequity is more distress than it's worth. The default output gamma correction value in Snow Leopard is now 2.2, just enjoy everyone else. Done and done.

    If they notice at all, users will likely suffer this change as a feeling that the Snow Leopard user interface has a bit more contrast than Leopard's. This is reinforced by the modern 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, precise to form, Apple could not resist adding a few graphical tweaks to the Snow Leopard interface. The most clear-cut changes are related to the Dock. First, there's the modern "spotlight" eye 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 bar no one at all pop-up menus on the Dock—and only on the Dock—have a unique eye 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 sure 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 modern eye for a lone (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 boom about that, and more. If the oath of Snow Leopard's appearance was to "first, attain no harm," then I consider 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 live these: everything fades. Apple has sprinkled Core Animation fairy dust over seemingly every application in Snow Leopard. If any share 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 live 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 treasure in Snow Leopard's visual changes.

    The one that really drove me over the edge is the fussy slight dance of the filename zone 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 tiny zone that makes me want to scream. And whether or not I'm actually waiting for these animations to finish before I can continue to employ my computer, it certainly feels that passage sometimes.

    Still, I must unenthusiastically forecast that most modest 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.


    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 modern features" to consumers, there's the issue of how to rate people to notice that this modern 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 bar no one at all 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 cleave and dried: outer space, stars, flush 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 eye 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 fence 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 beget been coalesced.)

    One of these things is not  enjoy the others…One of these things is not enjoy 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 beget one vast thing going for it: it's immediately recognizable as something modern 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 casual 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 modern product.

    (If you'd enjoy your own picture of Snowy the snow leopard (that's right, I've named him), Apple was kindhearted enough to comprise 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 bar no one at all 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 live missing out on the meat of this review and the heart of Apple's modern 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 support for the then-new PowerPC G5 64-bit CPU. In 2005, Tiger brought with it the competence to create precise 64-bit processes—as long as they didn't link with any of the GUI libraries. Finally, Leopard in 2007 included support for 64-bit GUI applications. But again, there was a caveat: 64-bit support extended to Cocoa applications only. It was, effectively, the conclude 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 compass 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, bar no one at all that yellow in the Snow Leopard diagram represents its capability, not necessarily its default mode of operation.


    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 very kind.

    An indispensable 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 comprise a 64-bit kernel, there'd live 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 bar no one at all of the devices commonly attached to an Xserve will live supported by 64-bit drivers supplied by Apple in Snow Leopard itself.

    Perhaps surprisingly, not bar no one at all 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 bar no one at all 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 bar no one at all K64-capable Macs, boot while holding down "6" and "4" keys simultaneously to select the 64-bit kernel. For a more permanent solution, employ 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 employ 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 employ the 64-bit kernel?

    The first intuition has to attain with RAM, and not in the passage you might think. Though Leopard uses a 32-bit kernel, Macs running Leopard can hold and employ far more RAM than the 4 GB circumscribe 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 enjoy a problem; after all, should the kernel really necessity more than 4GB of remembrance to attain its job? But recollect that share 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 enjoy a lot. But now consider a Mac in the not-too-distant future containing 96GB of RAM. (If this sounds ridiculous to you, consider of how ridiculous the 8GB of RAM in the Mac I'm typing on right now would beget 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 remembrance 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 necessity it today on the desktop, it's already common for servers to beget 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 occasion to leave behind some of the ugliness of the past and comprise more modern features: more registers, modern addressing modes, non-stack-based floating point capabilities, etc. K64 reaps these benefits. Apple makes the following claims about its performance:

  • 250% faster system convene entry point
  • 70% faster user/kernel remembrance copy
  • Focused benchmarking would endure these out, I'm sure. But in daily use, you're unlikely to live able to attribute any particular performance boost to the kernel. consider of K64 as removing bottlenecks from the few (usually server-based) applications that actually attain 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 beget 96GB of RAM installed, you would not risk starving the kernel of address space, and if you don't beget any 32-bit drivers that you absolutely necessity to use, then by bar no one at all means, boot into the 64-bit kernel.

    For everyone else, my counsel is to live cheerful that K64 will live ready and waiting for you when you eventually attain necessity it—and delight attain inspirit bar no one at all the vendors that get kernel extensions that you keeping about to add K64 support as soon as possible.

    Finally, this is worth repeating: delight support in intuition that you attain not necessity to flee the 64-bit kernel in order to flee 64-bit applications or install more than 4GB of RAM in your Mac. Applications flee 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 possible to install and capture edge of much more than 4GB of RAM.

    64-bit applications

    While Leopard may beget brought with it support 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 possible for third-party developers to produce 64-bit (albeit Leopard-only) GUI applications, very few have—sometimes due to hapless realities, but most often because there's been no honorable intuition to attain 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, serve Viewer, Installer, Terminal, Calculator—you designation it, it's 64-bit.

    The second vast carrot (or stick, depending on how you eye at it) is the continued necessity of 32-bit support for modern APIs and technologies. Leopard started the trend, leaving deprecated APIs behind and only porting the modern 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 modern 64-bit-only API is QuickTime X—significant enough to live addressed separately, so sojourn tuned.

    64-bits or bust

    All of this is Apple's not-so-subtle passage of telling developers that the time to jog to 64-bit is now, and that 64-bit should live the default for bar no one at all modern applications, whether a developer thinks it's "needed" or not. In most cases, these modern APIs beget no intrinsic connection to 64-bit. Apple has simply chosen to employ them as additional forms of persuasion.

    Despite bar no one at all of the above, I'd noiseless convene Snow Leopard merely the penultimate step in Mac OS X's journey to live 64-bit from top to bottom. I fully hope Mac OS X 10.7 to boot into the 64-bit kernel by default, to ship with 64-bit versions of bar no one at all 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 enjoy such a vast 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 swirl to fade 64-bit.

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

    To live clear, QuickTime the technology and QuickTime the brand will most definitely live coming to 64-bit. What's being left behind in 32-bit-only profile 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, enjoy the one in in Mac OS X, is pronounced "ten." This is but the first of many eerie parallels. enjoy Mac OS X before it, QuickTime X:

  • aims to get a clean shatter 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 indispensable features in its initial release
  • Maximum available Mac CPU  hasten (MHz)Maximum available Mac CPU hasten (MHz)

    Let's capture these one at a time. First, why is a clean shatter needed? rescue 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 right is meant to hammer home this point. Forward-thinking design can only rate you so far. The shape of the world a technology is born into eventually, inevitably dictates its fate. This is especially precise for long-lived APIs enjoy QuickTime with a tough bent towards backward compatibility.

    As the first successful implementation of video on a personal computer, it's frankly extraordinary that the QuickTime API has lasted as long as it has. But the world has moved on. Just as Mac OS found 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 honorable support for the GPU-accelerated video playback necessary to handle modern video codecs on a handheld (even with a CPU sixteen times the clock hasten 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 fitting comfortably within the RAM and CPU constraints of the iPhone.

    Hmm. An aging desktop video API in necessity of a replacement. A fresh, modern video library with honorable 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 impress the circumscribe between the traditional QuickTime 7 and the modern QuickTime X. It's done this in Snow Leopard by limiting bar no one at all employ of QuickTime by 64-bit applications to the QTKit Objective-C framework.

    QTKit's modern 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 employ QTKit as before, and behind the scenes QTKit will elect whether to employ QuickTime 7 or QuickTime X to fulfill each request.

    If QuickTime X is so much better, why doesn't QTKit employ it for everything? The reply is that QuickTime X, enjoy its Mac OS X namesake, has very limited capabilities in its initial release. While QuickTime X supports playback, capture, and exporting, it does not support general-purpose video editing. It besides supports only "modern" video formats—basically, anything that can live 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 support 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 support using a plug-in of any kind? You guessed it: QuickTime 7.

    But wait a second. If QTKit is the only passage for a 64-bit application to employ 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 support "mixed mode" processes that can execute both 32-bit and 64-bit code, then how the heck does a 64-bit process attain anything that requires the QuickTime 7 back-end?

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

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

    And the reply is revealed. When a 64-bit application using QTKit requires the services of the 32-bit-only QuickTime 7 back-end, QTKit spawns a part 32-bit QTKitServer process to attain the travail and communicate the results back to the originating 64-bit process. If you leave Activity Monitor open while using the modern QuickTime Player application, you can watch the QTKitServer processes near and fade as needed. This is bar no one at all handled transparently by the QTKit framework; the application itself necessity not live sensible of these machinations.

    Yes, it's going to live a long, long time before QuickTime 7 disappears completely from Mac OS X (at least Apple was kindhearted enough not to convene it "QuickTime Classic"), but the path forward is clear. With each modern release of Mac OS X, hope the capabilities of QuickTime X to expand, and the number of things that noiseless require QuickTime 7 to decrease. In Mac OS X 10.7, for example, I imagine that QuickTime X will gain support for plug-ins. And surely by Mac OS X 10.8, QuickTime X will beget complete video editing support. bar no one at all this will live 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 passage for a developer to request that QTKit employ the QuickTime X back-end, there are several circuitous means to influence the decision. The key is the QTKit API, which relies heavily on the concept of intent.

    QuickTime versions 1 through 7 employ a lone representation of bar no one at all media resources internally: a Movie object. This representation includes information about the individual tracks that get up the movie, the sample tables for each track, and so on—all the information QuickTime needs to understand and maneuver the media.

    This sounds worthy until you realize that to attain 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 protest representation of the MP3 file before it can open 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 get this process less painful by doing the scanning and parsing incrementally in the background. You can note this in many QuickTime-based player applications in the profile 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 zone from left to right.

    QuickTime 7 doing more  travail than necessary

    QuickTime 7 doing more travail than necessary

    Though playback can open almost immediately (provided you play from the beginning, that is) it's worthwhile to capture a step back and consider what's going on here. QuickTime is creating a Movie protest suitable for any operation that QuickTime can perform: editing, track extraction or addition, exporting, you designation it. But what if bar no one at all I want to attain is play the file?

    The distress is, the QuickTime 7 API lacks a passage to express this kindhearted of intent. There is no passage to boom to QuickTime 7, "Just open this file as quickly as possible so that I can play it. Don't bother reading every lone byte of the file from the disk and parsing it to determine its structure just in case I settle 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 passage to live eligible for the QuickTime X back-end at bar no one at all is to explicitly express your intent not to attain anything QuickTime X cannot handle. Furthermore, any attempt to fulfill an operation that lies outside your previously expressed intent will occasions QTKit to raise an exception.

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

    Indeed, there are many reasons to attain what it takes to rate 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 fritter time preparing its internal representation of the movie for editing and export when playback is bar no one at all 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 support 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 passage in recent years: steady, deliberate progress. Apple aims to ship no features before their time.

    As anxious as developers may live 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 cleave Studio. Thus far, It remains stuck in 32-bit. To boom that Apple is "highly motivated" to extend the capabilities of QuickTime X would live an understatement.

    Nevertheless, don't hope Apple to rush forward foolishly. Duplicating the functionality of a continually developed, 18-year-old API will not betide overnight. It will capture years, and it will live even longer before every indispensable Mac OS X application is updated to employ QTKit exclusively. Transitions. Gotta treasure '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 worthy view to employ as the only passage 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 noiseless being edited. When the application is instructed to rescue the file, if it only has the file path to travail with, it will conclude up creating a modern file in the traditional 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 serve 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 beget become the de facto representation for files that may live located somewhere other than the local machine. URLs can besides advert to local files, but in that case they beget bar no one at all the very disadvantages as file paths.

    This diversity of data types is reflected in Mac OS X's file system APIs. Some functions capture file path as arguments, some hope opaque references to files, and noiseless others travail only with URLs. Programs that employ these APIs often spend 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 bar no one at all levels of the operating system, and no lone one of them is comprehensive. To rate bar no one at all available information about a file on disk requires making several part calls, each of which may hope a different sort of file reference as an argument.

    Here's an instance Apple provided at WWDC. Opening a lone 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 lone data type: URLs. But these are URL "objects"—namely, the opaque data types NSURL and CFURL, with a toll-free bridge between them—that beget been imbued with bar no one at all the desirable attributes of an FSRef.

    Apple settled on these data types because their opaque nature allowed this kindhearted of enhancement, and because there are so many existing APIs that employ them. URLs are besides the most future-proof of bar no one at all the choices, with the scheme portion providing nearly unlimited flexibility for modern data types and access mechanisms. The modern file system APIs built around these opaque URL types support caching and metadata prefetching for a further performance boost.

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

    I mention bar no one at all of this not because I hope file system APIs to live bar no one at all that provocative to people without my particular fascination with this share of the operating system, but because, enjoy Core Text before it, it's an indication of exactly how juvenile Mac OS X really is as a platform. Even after seven major releases, Mac OS X is noiseless struggling to jog out from the shadow of its three ancestors: NeXTSTEP, classic Mac OS, and BSD Unix. Or perhaps it just goes to exhibit how ruthlessly Apple's core OS team is driven to supersede traditional and crusty APIs and data types with new, more modern versions.

    It will live a long time before the benefits of these changes trickle down (or is it up?) to end-users in the profile of Mac applications that are written or modified to employ these modern 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  honorable Mac OS X citizenTextEdit: a honorable Mac OS X citizen

    Of course, the key modifier here is "well-written." Simplifying the file system APIs means that more developers will live 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 elect to alter their existing, working application to employ these modern 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 hasten 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 live summed up in a lone "law", it would be, roughly, that the number of transistors that fitting onto a square inch of silicon doubles every 12 months.

    Moore later revised that to two years, but the time term is not what people rate 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 lone paper from 1965, but we'll rescue that aside for now. For a more thorough discussion of Moore's Law, delight read this classic article by Jon Stokes.)

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

    Moore's Law continues, at least for now, but their competence to get code flee faster with each modern increase in transistor density has slowed considerably. The free lunch is over. CPU clock speeds beget 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 live 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 noiseless got bar no one at all these modern transistors raining down on us, more every year. The challenge is to find modern ways to employ them to actually get computers faster.

    Thus far, the semiconductor industry's reply has been to give us more of what they already have. Where once a CPU contained a lone analytic processing unit, now CPUs in even the lowliest desktop computers hold two processor cores, with high-end models sporting two chips with eight analytic cores each. Granted, the cores themselves are besides getting faster, usually by doing more at the very clock hasten 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 flee your application twice as swiftly as a single-core CPU. In fact, your application probably won't flee any faster at bar no one at all unless it was written to capture edge of more than just a lone analytic CPU. Presented with a glut of transistors, chipmakers beget turned around and provided more computing resources than programmers know what to attain 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 passage for applications—and the OS itself—to utilize the ever-growing wealth of computing resources at their disposal. If I had to pick lone technological "theme" for Snow Leopard, this would live it: helping developers utilize bar no one at all this newfound silicon; helping them attain more with more.

    To that end, Snow Leopard includes two significant modern APIs backed by several smaller, but equally indispensable 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, delight entangle 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 live misled by its humble employ in Leopard; Apple has imposing 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 modern 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 modern 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 bar no one at all command-line and source-compatible—in theory, anyway. Clang does not yet support some of the more esoteric features of GCC. Clang besides only supports C, Objective-C, and a slight bit of C++ (Clang(uage), rate it?) whereas GCC supports many more. Apple is committed to full C++ support for Clang, and hopes to travail out the remaining GCC incompatibilities during Snow Leopard's lifetime.

    Clang brings with it the two headline attributes you hope in a hot, modern 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 enjoy Adium and Growl, Clang compiles nearly three times faster than GCC 4.2. As for the hasten 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 beget much to attain with taking edge of multiple CPU cores and so on, but it's sure to live the first thing that a developer actually notices when using Clang. Indulge me.

    For starters, Clang is embeddable, so Xcode can employ the very 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 lucid what the problem is, especially if you're modern to C programming. Yes, bar no one at all you hotshots already know what the problem is (especially if you saw this instance at WWDC), but I consider everyone can accord that this error, generated by Clang, is a lot more helpful:

    Clang  mistake message for an unknown type

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

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

    GCC  mistake message for  substandard operands

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

    Clang  mistake message for  substandard operands

    Sometimes the mistake is perfectly clear, but it just seems a bit off, enjoy 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 enjoy this means a lot to developers. And then there are the not-so-little things that signify even more, enjoy the LLVM-powered static analyzer. The image below shows how the static analyzer displays its discovery of a possible bug.

    OH HAI I found UR BUGOH HAI I found 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 sure Apple is going hog-wild running the static analyzer on bar no one at all of its applications and the operating system itself. The prospect of an automated passage to discover bugs that may beget 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 share 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 suffer apparently convinced Apple that it's unwise to reckon on a third party for its platform's evolution tools. Though it's taken many years, I consider even the most diehard Metrowerks fan would beget to accord that Xcode in Snow Leopard is now a pretty damn honorable IDE.

    After years of struggling with the disconnect between the goals of the GCC project and its own compiler needs, Apple has finally cleave the apron strings. OK, granted, GCC 4.2 is noiseless the default compiler in Snow Leopard, but this is a transitional phase. Clang is the recommended compiler, and the focus of bar no one at all 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 note in the following sections, LLVM's scaly, metallic head pops up in a few key places.


    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 beget 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 capture closures and anonymous functions for granted, those who travail with more traditional, statically compiled languages such as C and its derivatives may find them quite exotic. As for non-programmers, they likely beget no interest in this topic at all. But I'm going to attempt an explanation nonetheless, as blocks profile the foundation of some other provocative technologies to live discussed later.

    Perhaps the simplest passage to warrant blocks is that they get functions another profile of data. C-derived languages already beget function pointers, which can live passed around enjoy data, but these can only point to functions created at compile time. The only passage to influence the deportment of such a function is by passing different arguments to the function or by setting global variables which are then accessed from within the function. Both of these approaches beget vast disadvantages

    Passing arguments becomes cumbersome as their number and complexity grows. Also, it may live that you beget limited control over the arguments that will live passed to your function, as is often the case with callbacks. To compensate, you may beget to bundle up bar no one at all of your provocative situation into a context protest of some kind. But when, how, and by whom that context data will live disposed of can live difficult to pin down. Often, a second callback is required for this. It's bar no one at all quite a pain.

    As for the employ of global variables, in addition to being a well-known anti-pattern, it's besides not thread-safe. To get it so requires locks or some other profile of mutual exclusion to obviate multiple invocations of the very function 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 bar no one at all of these problems by allowing functional blobs of code—blocks—to live 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) { recrudesce a * b };

    Here I've created a function named multiplier that takes a lone 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 convene to multiplier(5) would recrudesce the value 10.

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

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

    /* A function that takes a lone integer dispute and returns a pointer to a function that takes two integer arguments and returns a floating-point number. */ float (*func2(int a))(int, int); /* A function that takes a lone integer dispute and returns a shroud that takes two integer arguments and returns a floating-point number. */ float (^func1(int a))(int, int);

    You'll just beget to faith me when I inform you that this syntax actually makes sense to seasoned C programmers.

    Now then, does this signify that C is suddenly a dynamic, high-level language enjoy JavaScript or Lisp? Hardly. The existing distinction between the stack and the heap, the rules governing automatic and static variables, and so on are bar no one at all noiseless in full effect. Plus, now there's a gross modern set of rules for how blocks interact with each of these things. There's even a modern __block storage sort attribute to further control the scope and lifetime of values used in blocks.

    All of that said, blocks are noiseless a huge win in C. Thanks to blocks, the friendlier APIs long enjoyed by dynamic languages are now possible in C-derived languages. For example, suppose you want to apply some operation to every line in a file. To attain so in a low-level language enjoy C requires some amount of boilerplate code to open and read from the file, handle any errors, read each line into a buffer, and clean 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 share in bold is an abstract representation of what you're planning to attain to each line of the file. The leisure 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 enjoy to live able to attain is factor it out into a function that you can call. But then you're faced with the problem of how to express the operation you'd enjoy to fulfill on each line of the file. In the middle of each shroud of boilerplate may live many lines of code expressing the operation to live applied. This code may reference or modify local variables which are affected by the runtime deportment of the program, so traditional function pointers won't work. What to do?

    Thanks to blocks, you can define a function that takes a filename and a shroud as arguments. This gets bar no one at all 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 dispute after filename is a literal shroud that takes a line of text as an argument.

    Even when the volume of boilerplate is small, the simplicity and clarity premium is noiseless worthwhile. consider the simplest possible 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 live more complicated than the sentence describing it. attain something 10 times! I never want to screw that up again. Blocks can help. If they just invest a slight pains 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 exile the bug for good. Now, repeating any arbitrary shroud of code a specific number of times is bar no one at all but idiot-proof:

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

    And remember, the shroud dispute to repeat() can hold exactly the very kindhearted of code, literally copied and pasted, that would beget appeared within a traditional for loop.

    All these possibilities and more beget 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 modern APIs that employ blocks in Snow Leopard. Many of these APIs would not live possible at bar no one at all without blocks, and bar no one at all of them are more elegant and concise than they would live otherwise.

    It's Apple goal to submit blocks as an official extension to one or more of the C-based languages, though it's not yet lucid which standards bodies are receptive to the proposal. For now, blocks are supported by bar no one at all four of Apple's compilers in Mac OS X.

    Concurrency in the real world: a prelude

    The struggle to get efficient employ of a great number of independent computing devices is not new. For decades, the bailiwick of high-performance computing has tackled this problem. The challenges faced by people writing software for supercomputers many years ago beget 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, live Inc. was formed around the view 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, live created the BeBox, a dual-CPU desktop computer, and BeOS, a brand-new operating system.

    The signature entangle 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 get me exhibit another graph) could play multiple videos simultaneously while besides playing several audio tracks from a CD—some backwards— and bar no one at all the while, the user interface remained completely responsive.

    Let me inform you, having lived through this term myself, the suffer 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 suffer noiseless doesn't match the responsiveness of BeOS. This is certainly precise emotionally, if not necessarily literally.

    After nearly purchasing live in the late 1990s, Apple bought NeXT instead, and the leisure is history. But had Apple gone with contrivance live instead, Mac developers might beget had a harsh road ahead. While bar no one at all that pervasive multithreading made for impressive technology demos and a worthy user experience, it could live extremely demanding on the programmer. BeOS was bar no one at all about threads, going so far as to maintain a part thread for each window. Whether you liked it or not, your BeOS program was going to live multithreaded.

    Parallel programming is notoriously hard, with the manual management of POSIX-style threads representing the abysmal conclude of that pool. The best programmers in the world are hard-pressed to create great multithreaded programs in low-level languages enjoy C or C++ without finding themselves impaled on the spikes of deadlock, race conditions, and other perils inherent in the employ of in multiple simultaneous threads of execution that share the very remembrance 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 beget been invented for multithreaded programming.

    Nineteen years after live 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 lone glowing tower in a sea of sixteen otherwise vacuous lanes on a CPU monitor window.

    A wide-open  modest of transistorsA wide-open modest of transistors

    And woe live 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 modern user inputs are being pulled off the event queue by the application. A few seconds of that and an traditional friend makes its appearance: the spinning beach ball of death.


    Nooooooooo!!! Image from The Iconfactory

    This is the enemy: hardware with more computing resources than programmers know what to attain with, most of it completely idle, and bar no one at all the while the user is utterly blocked in his attempts to employ 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 reply to the concurrency conundrum is called imposing Central Dispatch (GCD). As with QuickTime X, the designation is extremely apt, though this is not entirely lucid until you understand the technology.

    The first thing to know about GCD is that it's not a modern Cocoa framework or similar special-purpose frill off to the side. It's a modest 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 necessity to link in a modern library to employ 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 live used from bar no one at all 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 enjoy the checkout line at the supermarket, for those who don't know and don't want to result the link.) Dequeuing the chore means handing it off to a thread where it will execute and attain its actual work.

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

    A imposing Central Dispatch queue in action

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

    But first, let's eye at the other kindhearted of queue. A serial queue works just enjoy a modest queue, except that it only executes one chore at a time. That means chore completion in a serial queue is besides FIFO. Serial queues can live created explicitly, just enjoy modest 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 travail needs to live done, and disappearing as they're no longer needed. Where attain these threads near from and where attain they fade 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 flee on a thread, the thread goes back into the pool.

    This is an extremely indispensable 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 spend a significant amount of time simply shuffling threads in and out of the available processor cores.

    Let's boom a program has a problem that can live 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 reply 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 fritter 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 hope to beget the entire machine to themselves when they run, there's no passage 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 rescue in flight at any given time is best determined by a single, globally sensible entity. In Snow Leopard, that entity is GCD. It will support zero threads in its pool if there are no queues that beget tasks to run. As tasks are dequeued, GCD will create and dole out threads in a passage that optimizes the employ 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 chore ready to live 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 bar no one at all 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 remembrance 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 beget 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 remembrance overhead, they're besides relatively costly to create. Creating a modern thread for each chore would live the worst possible scenario. Every time GCD can employ a thread to execute more than one task, it's a win for overall system efficiency.

    Remember the problem of the programmer trying to device out how many threads to create? Using GCD, he doesn't beget 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 employ 500 concurrent tasks, then he can fade ahead and create 500 GCD queues and ration his travail among them. GCD will device out how many actual threads to create to attain the work. Furthermore it will adjust the number of threads dynamically as the conditions on the system change.

    But perhaps most importantly, as modern hardware is released with more and more CPU cores, the programmer does not necessity to change his application at all. Thanks to GCD, it will transparently capture edge of any and bar no one at all 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 live arranged in arbitrarily intricate directed acyclic graphs. (Actually, they can live cyclic too, but then the deportment is undefined. Don't attain that.) Queue hierarchies can live used to funnel tasks from disparate subsystems into a narrower set of centrally controlled queues, or to obligate a set of modest queues to delegate to a serial queue, effectively serializing them bar no one at all 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 live suspended, resumed, and cancelled. Queues can besides live grouped, allowing bar no one at all tasks distributed to the group to live tracked and accounted for as a unit.

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


    Okay, so GCD is a worthy passage to get efficient employ 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 contradictory conclude of the spectrum from BeOS's "pervasive multithreading" design. Rather than achieving responsiveness by getting every possible component of an application running concurrently on its own thread (and paying a heavy charge in terms of intricate data sharing and locking concerns), GCD encourages a much more limited, hierarchical approach: a main application thread where bar no one at all 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 consider about how best to split the travail of their application into multiple concurrent threads (though when they're ready to attain that, GCD will live willing and able to help). At its most basic level, GCD aims to inspirit developers to jog from thinking synchronously to thinking asynchronous. Something enjoy this: "Write your application as usual, but if there's any share of its operation that can reasonably live expected to capture more than a few seconds to complete, then for the treasure of Zarzycki, rate 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 attain they noiseless note the beach ball in Mac OS X applications? Why don't bar no one at all applications already execute bar no one at all of their potentially long-running tasks on background threads?

    A few reasons beget been mentioned already (e.g., the vicissitude of knowing how many threads to create) but the vast 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 shatter from coding the actual travail of your application to coding bar no one at all this task-management plumbing. And so, especially in borderline cases, enjoy an operation that may capture 3 to 5 seconds, developers just attain it synchronously and jog onto the next thing.

    Unfortunately, there's a surprising number of very common things that an application can attain that execute quickly most of the time, but beget the potential to capture 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 live theme to a very long (or at least an "unexamined-by-the-application-developer") timeout. The very goes for designation lookups (e.g., DNS or LDAP), which almost always execute instantly, but entangle many applications completely off-guard when they start taking their sweet time to recrudesce a result. Thus, even the most meticulously constructed Mac OS X applications can conclude up throwing the beach ball in their puss from time to time.

    With GCD, Apple is maxim it doesn't beget to live this way. For example, suppose a document-based application has a button that, when clicked, will resolve the current document and panoply some provocative 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 function cadaver 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 live updated to reflect this modern state. It bar no one at all follows a very common pattern, and it works worthy as long as no one at all of these steps—which are bar no one at all running on the main thread, remember—takes too long. Because after the user presses the button, the main thread of the application needs to handle that user input as swiftly as possible so it can rate back to the main event loop to process the next user action.

    The code above works worthy until a user opens a very great or very intricate document. Suddenly, the "analyze" step doesn't capture 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 great file. And anyway, I really don't want to start reading documentation about threads and adding bar no one at all 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 jog the document analysis to the background by adding just two lines of code (okay, and two lines of closing braces), bar no one at all located within the existing function? No application-global objects, no thread management, no callbacks, no dispute marshalling, no context objects, not even any additional variables. Behold, imposing 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. bar no one at all of the functions in GCD open with dispatch_, and you can note four such calls in the blue lines of code above. The key to the minimal invasiveness of this code is revealed in the second dispute 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 competence of blocks to capture the surrounding context is what allows these GCD calls to live dropped right into some existing code without requiring any additional setup or re-factoring or other contortions in service of the API.

    But the best share of this code is how it deals with the problem of detecting when the background chore completes and then showing the result. In the synchronous code, the resolve mode convene and the code to update the application panoply simply issue in the desired sequence within the function. In the asynchronous code, miraculously, this is noiseless the case. Here's how it works.

    The outer dispatch_async() convene puts a chore on a global concurrent GCD queue. That task, represented by the shroud passed as the second argument, contains the potentially time-consuming resolve mode call, plus another convene to dispatch_async() that puts a chore 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 bar no one at all live done from the main thread in a Cocoa application, so the code in the inner shroud could not live executed anywhere else. But rather than having the background thread transmit some kindhearted of special-purpose notification back to the main thread when the resolve mode convene completes (and then adding some code to the application to detect and handle this notification), the travail that needs to live done on the main thread to update the panoply is encapsulated in yet another shroud within the larger one. When the resolve convene is done, the inner shroud is rescue onto the main queue where it will (eventually) flee on the main thread and attain its travail of updating the display.

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

    Believe it or not, it's just as facile to capture a serial implementation of a string of independent operations and parallelize it. The code below does travail on import elements of data, one after the other, and then summarizes the results once bar no one at all the elements beget 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 part chore for each factor onto a global concurrent queue. (Again, it's up to GCD to settle how many threads to actually employ 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 beget 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 travail required to wait for bar no one at all the independent tests to complete. (The dispatch_apply() convene will not recrudesce until bar no one at all the tasks it has dispatched beget completed.) Stunning.

    Grand Central Awesome

    Of bar no one at all the APIs added in Snow Leopard, imposing Central Dispatch has the most far-reaching implications for the future of Mac OS X. Never before has it been so facile to attain travail asynchronously and to spread workloads across many CPUs.

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

    But imposing Central Dispatch doesn't actually address this issue at all. It offers no serve whatsoever in deciding how to split your travail up into independently executable tasks—that is, deciding what pieces can or should live executed asynchronously or in parallel. That's noiseless entirely up to the developer (and noiseless a tough problem). What GCD does instead is much more pragmatic. Once a developer has identified something that can live split off into a part task, GCD makes it as facile and non-invasive as possible to actually attain so.

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

    One of Apple's slogans for imposing Central Dispatch is "islands of serialization in a sea of concurrency." That does a worthy job of capturing the practical reality of adding more concurrency to run-of-the-mill desktop applications. Those islands are what segregate 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 live better executed off the main thread, even if they're made up of several sequential or otherwise partially interdependent tasks. GCD makes it facile to shatter off the entire unit of travail while maintaining the existing order and dependencies between subtasks.

    Those with some multithreaded programming suffer may live unimpressed with the GCD. So Apple made a thread pool. vast 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 imposing Central Dispatch so attractive to developers. Just as Time Machine was "the first backup system people will actually use," imposing Central Dispatch is poised to finally spread the heretofore gloomy expertise of asynchronous application design to bar no one at all 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 indispensable modern language feature, and a powerful, pragmatic concurrency API built on top of the modern compilers' support for said language feature. bar no one at all this goes a long passage towards helping developers and the OS itself get maximum employ 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 inform the tale. While Mac CPUs hold up to four cores (which may exhibit up as eight analytic cores thanks to symmetric multithreading), high-end GPUs hold 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 enjoy CPUs, GPUs now near 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 beget evolved from the fixed-function silicon of their ancestors that could not live programmed directly at all. They don't support the flush set of instructions available on CPUs, the maximum size of the programs that will flee is often limited and very small, and not bar no one at all of the features of the industry-standard IEEE floating-point computation specification are supported.

    Today's GPUs can live programmed, but the most common forms of programmability are noiseless 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 honorable fitting for GPU hardware. It would live 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 sort of execution units, available data formats, instruction sets, remembrance architecture, you designation it. Programmers don't want to live exposed to these differences, but it's difficult to travail around the complete necessity 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 remembrance hierarchy, and several bundled computational libraries. CUDA is but one entrant in the burgeoning GPGPU bailiwick (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 attain the very for general-purpose computation. In fact, OpenCL is supported by the very consortium as OpenGL: the ominously named Khronos Group. But get no mistake, OpenCL is Apple's baby.

    Apple understood that OpenCL's best casual of success was to become an industry standard, not just an Apple technology. To get 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 bar no one at all near together.

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

    The OpenCL difference

    This is bar no one at all well and good, but to beget any repercussion on the day-to-day life of Mac users, developers actually beget to employ OpenCL in their applications. Historically, GPGPU programming languages beget not seen much employ in traditional desktop applications. There are several reasons for this.

    Early on, writing programs for the GPU often required the employ of vendor-specific assembly languages that were far removed from the suffer of writing a typical desktop application using a contemporaneous 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 noiseless could not live bothered to navigate this queer world.

    And even if the GPU did give a huge hasten 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 found in laptops, cannot flee languages enjoy CUDA at all.

    Apple's key decision in the design of OpenCL was to allow OpenCL programs to flee not just on GPUs, but on CPUs as well. An OpenCL program can query the hardware it's running on and enumerate bar no one at all 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 possible to create a lone analytic device consisting of any combination of eligible computing resources: two GPUs, a GPU and two CPUs, etc.

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

    Certain kinds of algorithms actually flee 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 beget to flee 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 live a real pain. There's MMX, SSE, SSE2, SSE3, and SSE4 to deal with, bar no one at all with slightly different capabilities, and bar no one at all of which obligate the programmer to write code enjoy this:

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

    OpenCL's endemic support for vector types de-clutters the code considerably:

    r1 = m1 * (x1 + x2);

    Similarly, OpenCL's support for implicit parallelism makes it much easier to capture edge of multiple CPU cores. Rather than writing bar no one at all the logic to split your data into pieces and ration those pieces to the parallel-computing hardware, OpenCL lets you write just the code to operate on a lone piece of the data and then transmit it, along with the entire shroud of data and the desired smooth of parallelism, to the computing device.

    This arrangement is taken for granted in traditional graphics programming, where code implicitly works on bar no one at all pixels in a texture or bar no one at all vertices in a polygon; the programmer only needs to write code that will exist in the "inner loop," so to speak. An API with support for this kindhearted of parallelism that runs on CPUs as well as GPUs fills an indispensable gap.

    Writing to OpenCL besides future-proofs task- or data-parallel code. Just as the very OpenGL code will rate faster and faster as newer, more powerful GPUs are released, so too will OpenCL code fulfill better as CPUs and GPUs rate 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 capture edge of them, just as video card makers and OS vendors update their OpenGL drivers to capture edge of faster GPUs. Meanwhile, the application developer's code remains unchanged. Not even a recompile is required.

    Here live dragons (and trains)

    How, you may wonder, can the very compiled code conclude 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 attain 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 order for the requested smooth of parallelism by creating and distributing threads appropriately to the available cores.

    Well, wouldn't you know it? Apple just happens to beget two technologies that resolve 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 lone code generator for each target instruction set, and concentrate bar no one at all of its pains on a lone device-independent code optimizer. There's no longer any necessity 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, recollect Core Image? That's another API that needs to compile code just-in-time and ship it off to execute on parallel hardware enjoy GPUs and multi-core CPUs. In Snow Leopard, Core Image has been re-implemented using OpenCL, producing a hefty 25% overall performance boost.)

    To handle chore parallelism and provision threads, OpenCL is built on top of imposing Central Dispatch. This is such a natural fitting that it's a bit surprising that the OpenCL API doesn't employ blocks. I consider Apple decided that it shouldn't press its luck when it comes to getting its home-grown technologies adopted by other vendors. This decision already seems to live paying off, as AMD has its own OpenCL implementation under way.

    The top of the pyramid

    Though the underlying technologies, Clang, blocks and imposing Central Dispatch, will undoubtedly live more widely used by developers, OpenCL represents the culmination of that particular technological thread in Snow Leopard. This is the gold gauge of software engineering: creating a modern public API by structure 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 noiseless exist in numbers that are orders of magnitude lower than the hundreds of processing units in modern GPUs. On the other hand, GPUs noiseless beget a ways to fade to entangle up with the power and flexibility of a full-fledged CPU core. But even with bar no one at all the differences, writing code exclusively for either one of those worlds noiseless smacks of leaving money on the table.

    With OpenCL in hand, there's no longer a necessity to rescue bar no one at all your eggs in one silicon basket. And with the advent of hybrid CPU/GPU efforts enjoy Intel's Larabee, which employ CPU-caliber processing engines, but in much higher numbers, OpenCL may prove even more indispensable 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 live arduous for end-users to rate excited about "plumbing" technologies enjoy imposing Central Dispatch and OpenCL, let lonesome 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 live because they stand on the shoulders of giants.

    QuickTime Player's  modern icon (Not a fan)QuickTime Player's modern 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 necessity 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 sense of the word "QuickTime" in the minds of consumers—have blurred the picture somewhat.

    The first head-scratcher occurs during installation. If you betide to click on the "Customize…" button during installation, you'll note 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 live an optional install?

    Well, there's no necessity to panic. That item in the installer should actually read "QuickTime Player 7." QuickTime 7, the traditional 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 traditional blue "Q" icon, the one that many casual users actually consider of as being "QuickTime," that's been replaced with a modern QuickTime-X-savvy version sporting a pudgy modern icon (see above right).

    The modern player application is a vast 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 traditional QuickTime Player, replaced by a frameless window with a black title bar and a floating, moveable set of controls.

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

    It's enjoy a combination of the window treatment of the excellent NicePlayer application and the full-screen playback controls from the traditional QuickTime Player. I'm a bit bothered by two things. First, the ever-so-slightly clipped corners seem enjoy a substandard idea. Am I just hypothetical 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 share of the frame? Yes, you can jog 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 live moved. I appreciate the compactness of this approach, but it'd live nice if the title bar overlap could live disabled and the controls could live dragged off the movie entirely and docked to the bottom or something.

    (One blessing for people who share my OCD tendencies: if you jog the floating controls, they don't recollect their position the next time you open a movie. Why is that a blessing? Because if it worked the other way, we'd bar no one at all spend passage too much time fretting about their inability to restore the controller to its default, precisely centered position. Sad, but true.)

    The modern 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 profile a timeline, with adjustable stops at each conclude for trimming.

    Trimming in the  modern QuickTime Player Enlarge / Trimming in the modern 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 beget to sensation exactly how useful the fancy timeline appearances are. The audio waveform is quite tiny and compressed, and the limited horizontal space of the in-window panoply means a movie can only exhibit a handful of video frames in its timeline. Also, if there's any competence to attain fine adjustments using something other than extremely watchful mouse movements (which are necessarily theme to a limited resolution) then I couldn't find it. Final cleave Pro this is not.

    QuickTime Player has erudite another modern trick: screen recording. The controls are limited, so more demanding users will noiseless beget a necessity 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 modern QuickTime Player has the competence 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 attain with the modern 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. bar no one at all of these things were possible with the traditional 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 attribute their absence in the modern QuickTime Player to the previously discussed limitations of QuickTime X. But the modern 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 enjoy trimming, plus some previously "Pro"-only features enjoy full-screen playback. Also, the modern 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 amaze waiting for you if you install the optional QuickTime Player 7. When I did so, what I got was the traditional QuickTime Player—somewhat insultingly installed in the "Utilities" folder—with bar no one at all of its "Pro" features permanently unlocked. Yes, the tyranny of QuickTime Pro seems to live 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 beget bar no one at all "pro" features unlocked for everyone. I installed Snow Leopard onto an vacuous 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 bar no one at all pro features unlocked and with no visible QuickTime Pro registration information. I did, however, beget 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 modern appearance of some aspects of the Dock are accompanied by some modern 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 very result. You can then continue that very 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 rate in the habitude of doing it.

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

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

    In the screenshot above, you'll notice that no one at all of the minimized windows issue in my Dock. That's thanks to another welcome addition: the competence 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 rate 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 fitting 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 tiny "back" navigation button appears once you descend.

    These are bar no one at all useful modern behaviors, and quite a premium considering the hypothetical "no modern 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 noiseless either sacrifice some functionality (e.g., Dock icon badges and bounce notifications) or continue to employ the Dock in addition to a third-party application.

    The option to support 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 beget it open in the Finder, while besides retaining the competence to drag items into that folder. This was the default deportment for docked folders for the first six years of Mac OS X's life, but it changed in Leopard. Snow Leopard does not help matters.

    Docking an alias to a folder provides the single-click-open behavior, but items cannot live 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 item to a docked folder alias looks enjoy it will travail (the icon highlights) but upon release, the dragged item simply springs back to its original location. I really hoped this one would rate 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 exhibit that its version number had been updated to 10.6. The more provocative 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 substandard 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 necessity is a Cocoa Finder! Surely that will resolve bar no one at all their woes." Well, Snow Leopard features a 64-bit Finder, and as they bar no one at all 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 modern features… except for maybe one or two. And so, the "new" Cocoa Finder looks and works almost exactly enjoy the traditional Carbon Finder. The biggest indicator of its "Cocoa-ness" is the extensive employ 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 profile its modern shape.

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

    The number-one feature request from heavy column-view users has finally been implemented: sortable columns. The sort order applies to bar no one at all 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 live set using a menu command (each of which has a keyboard shortcut) or by right-clicking in an unoccupied zone 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 tiny slider to control the size of the icons.

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

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

    The icon previews themselves beget been enhanced to better match the abilities available in Quick Look. rescue it bar no one at all together and you can smoothly zoom a tiny PDF icon, for example, into the impressively high-fidelity preview shown below, complete with the competence to swirl pages. One press of the space bar and you'll progress to the even larger and more supple Quick eye 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 beget 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 rate icon view to stick for the windows where it's most useful, I consider that odd slight slider is actually going to rate 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 zone for each list view item now spans the entire line. In Leopard, though the entire line was highlighted, only the file designation or icon portion could live 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 sure whether this change in deportment is intentional or if it's just an unexamined consequence of the underlying control used for list view in the modern 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 fitting the widest value in the column. Date headers will progressively shrink to exhibit 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 travail 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 beget been clamoring for year after year. There's now a preference to select the default scope of the search bailiwick in the Finder window toolbar. Can I rate 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 fade a long passage towards making the desktop environment feel more solid. A honorable 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 spurn to dismiss a disk if your current working directory in a command-line shell is on that disk. kindhearted of cool, but besides kindhearted of annoying.)

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

    Forcible ejection in progressForcible ejection in progress

    Hm, but why did I rate information about the offending application in one dialog, an option to obligate 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 device it out the old-fashioned way.)


    So does the modern Cocoa Finder finally exile bar no one at all 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 note it? If not, eye closer at the order of the dates in the supposedly sorted "Date Modified" column. So yeah, that traditional 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 awe that one of these files will someday rate a 200-character filename that will overlap with a neighboring file's name.

    The worst incarnation of this deportment happens along the right edge of the screen where mounted volumes issue on the desktop. (Incidentally, this is not the default; if you want to note disks on your desktop, you must enable this preference in the Finder.) When I mount a modern disk, I'm often surprised to note where it ends up appearing. If there are any icons remotely close to the right edge of the screen, the disk icon will spurn to issue there. Again, the Finder is not avoiding any actual designation or icon overlapping. It appears to live 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 rate to its pre-Snow-Leopard feature set and smooth of polish, it's quite an achievement for a Cocoa Finder to match or exceed its predecessor in its very first release. I'm sure the Carbon vs. Cocoa warriors would beget had a bailiwick day with that statement, were Carbon not rescue out to pasture in Leopard. But it was, and to the victor fade the spoils.


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

    The vast caveat is that it will only travail with a server running Exchange 2007 (Service Pack 1, Update Rollup 4) or later. While I'm sure Microsoft greatly appreciates any additional upgrade revenue this decision provides, it means that for users whose workplaces are noiseless 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 tight 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 support seems to travail as expected. I had to beget 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, bar no one at all I had to enter in the Mail application was my full name, e-mail address, and password, and it automatically discovered bar no one at all apropos settings and configured iCal and Address engage for me.

    Exchange setup: surprisingly easyExchange setup: surprisingly easy

    Windows users are no doubt accustomed to this kindhearted 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 found 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 rate the job done.

    Meeting availability checker Enlarge / Meeting availability checker

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

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


    The thing is, there's not really much to boom about performance in Snow Leopard. Dozens of benchmark graphs lead to the very 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 disclose some impressive numbers, it's the passage these tiny changes combine to help the real-world suffer 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 support for overlapping i/o. Spotlight indexing, which happens on Time Machine volumes as well, was identified as another time-consuming chore involved in backups, so its performance was improved. The networking code was enhanced to capture edge 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 endemic HFS+ file systems, Apple added support 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 hasten of an initial Time Machine backup. And, of course, the performance improvements to the individual subsystems profit bar no one at all applications that employ them, not just Time Machine.

    This holistic approach to performance improvement is not likely to knock anyone's socks off, but every time you flee 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 signify the time between the selection of the Shutdown or Restart command and when the system turns off or begins its modern boot cycle. Leopard doesn't capture long at bar no one at all to attain this; only a few dozen of seconds when there are no applications open. But in Snow Leopard, it's so swiftly 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 noiseless dwarf Snow Leopard's speedup, but that's mostly because Mac OS X was so excruciatingly sluggish in its early years. It's facile to create a vast 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 bar no one at all the more impressive.

    And yes, for the seventh consecutive time, a modern release of Mac OS X is faster on the very hardware than its predecessor. (And for the first time ever, it's smaller, too.) What more can you demand for, really? Even that traditional 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 traditional days—and quake it as swiftly as you can. Your cursor will never live more than a few millimeters from the window's grab handle; it tracks your frantic motion perfectly. On most Macs, this is actually precise in Leopard as well. It just goes to exhibit how far Mac OS X has near on the performance front. These days, they bar no one at all just capture it for granted, which is exactly the passage 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 kindhearted of "all grab bag," if you know what I mean. Apple's even got its own incarnation in the profile of a giant webpage of "refinements." I'll probably overlap with some of those, but there'll live a few modern ones here as well.

    New columns in open/save dialogs

    The list view in open and rescue dialog boxed now supports more than just "Name" and "Date Modified" columns. Right-click on any column to rate a election of additional columns to display. I've wanted this feature for a long time, and I'm cheerful 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 competence to talk to a wide compass of scanners. I plugged in my Epson Stylus CX7800, a device that previously required the employ of third-party software in order to employ 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 substandard slight scanning application. It has pretty honorable automatic protest detection, including support for multiple objects, obviating the necessity to manually crop items. Given the sometimes-questionable attribute of third-party printer and scanner drivers for Mac OS X, the competence to employ a bundled application is welcome.

    System Preferences bit wars

    System Preferences, enjoy virtually bar no one at all 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 bar no one at all installed preference panes, 64-bit or 32-bit. But if you click on a 32-bit preference pane, you'll live presented with a notification enjoy 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 bar no one at all of the first-party preference panes are compiled for both 64-bit and 32-bit operation, System Preferences does not necessity to relaunch again for the duration of its use. This raises the question, why not beget System Preferences launch in 32-bit mode bar no one at all the time? I suspect it's just another passage 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 indispensable to the Web suffer that relaunching in 32-bit mode is not really an option. You'd probably necessity to relaunch as soon as you visited your first webpage. But Apple does want Safari to flee 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 flee 32-bit plug-ins in part 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 profit 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 bar no one at all crashes of bar no one at all applications in Mac OS X. (And though it was not mentioned by name, I consider they bar no one at all know the primary culprit.)

    As you can note above, the QuickTime browser plug-in gets the very treatment as glisten and other third-party 32-bit Safari plug-ins. bar no one at all 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 casual to function correctly.

    While this is noiseless 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 live believed, isolating plug-ins may generate most of the profit of truly part 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 dismal to boom that resolution independence was obviously not a priority in Snow Leopard, because it hasn't gotten any better, and may beget actually regressed a bit. Here's what TextEdit looks enjoy 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 noiseless recollect Apple advising developers to beget 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 bar no one at all the time. On the other hand, it's not enjoy 200-DPI monitors are raining from the sky either. But I'd really enjoy to note Apple rate going on this. It will undoubtedly capture a long time for everything to eye and travail correctly, so let's rate started.

    Terminal splitters

    The Terminal application in Tiger and earlier versions of Mac OS X allowed each of its windows to live split horizontally into two part 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 rate on board the train to splittersville.)

    Terminal in Snow Leopard besides defaults to the modern Menlo font. But balky to earlier reports, the One precise Monospaced Font, Monaco, is most definitely noiseless 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 part "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 removed future, perhaps Apple will finally arrive at the "ultimate" arrangement of preference panes and they can bar no one at all finally fade more than two years without their muscle remembrance being disrupted.

    Before moving on, System Preferences has one well-kept 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. kindhearted of creepy, but useful.

    Core location

    One more gift from the iPhone, Core Location, allows Macs to device 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 flee 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 enjoy to leave my Mac Pro turned on 24 hours a day, especially during the summer in my un-air-conditioned house. But I attain want to beget access to the files on my Mac when I'm elsewhere—at work, on the road, etc. It is possible to wake a sleeping Mac remotely, but doing so requires being on the very local network.

    My solution has been to leave a smaller, more power-efficient laptop on at bar no one at all times on the very 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 live checked in the "Energy Saver" preference pane in System Preferences.)

    Snow Leopard provides a passage to attain this without leaving any of my computers running bar no one at all day. When a Mac running Snow Leopard is rescue to sleep, it attempts to hand off ownership of its IP address to its router. (This only works with an AirPort Extreme groundwork 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 bar no one at all my Macs asleep and noiseless beget access to their contents anytime, anywhere.

    Back to my hack

    As has become traditional, this modern 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 rate the worst of it. They've actually been unsupported and non-functional in 64-bit applications since Leopard. That wasn't such a vast 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 necessity of an officially sanctioned extension mechanism, developers looking to enhance its functionality beget most often resorted to the employ 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 possible 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 obligate users to do.

    Happily, at least one commonly used Safari enhancement has the honorable fortune to live built on top of the officially supported browser plug-in API used by Flash, QuickTime, etc. But that may not live 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 contrivance to flee Safari in its default 64-bit mode, I'll really miss Saft, a Safari extension I employ 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 eye up "noodles" in Wikipedia). I'm hoping that clever developers will find a passage to overcome this modern 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 shatter with each major operating system update as a matter of course. And each time, those determined fellows at Unsanity, against bar no one at all odds, manage to support 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 beget to wait too long for a Snow-Leopard-compatible version.

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


    It looks enjoy we'll bar no one at all live 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, support 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 indispensable and likely will near 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 impeccable fitting for Time Machine, but the most indispensable is its competence to transmit only the block-level changes during each backup. As Time Machine is currently implemented, if you get a tiny 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 great 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 demand what, exactly, is wrong with HFS+. Aside from its obvious necessity 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 live 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 part locations on the disk) and to allow for better concurrency.

    Practically speaking, consider about those times when you flee 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 betide 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 bar no one at all the time with HFS+ disks in Mac OS X when various bits of metadata rate corrupted or become out of date.

    Apple gets by year after year, tacking modern features onto HFS+ with duct tape and a prayer, but at a sure point there simply has to live 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 convivial exercise as a technological one. Creating a platform, even more so. bar no one at all of Snow Leopard's considerable technical achievements are not just designed to profit users; they're besides intended to goad, persuade, and otherwise herd developers in the direction that Apple feels will live most advantageous for the future of the platform.

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

    The usual passage to overcome this kindhearted of upgrade hesitation has been to pack the OS with modern features. modern features sell, and the more copies of the modern operating system in use, the more motivated developers are to update their applications to not just flee on the modern OS, but besides capture edge of its modern abilities.

    A major operating system upgrade with "no modern features" must play by a different set of rules. Every party involved expects some counterbalance to the necessity of modern features. In Snow Leopard, developers stand to reap the biggest benefits thanks to an impressive set of modern 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 get it facile for developers to jog 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 beget already been reports of modern bugs introduced to existing APIs in Snow Leopard. This is the exact contradictory of Snow Leopard's implied vow to users and developers that it would concentrate on making existing features faster and more robust without introducing modern functionality and the accompanying modern bugs.

    On the other side of the coin, I imagine bar no one at all the teams at Apple that worked on Snow Leopard absolutely reveled in the occasion 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 live this kindhearted of release valve every few years, lest the entire code groundwork fade off into the weeds.

    There's been one other "no modern 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 employ 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 attain 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 live sure that bar no one at all the software you keeping about is compatible. But don't wait too long, because at $29 for the upgrade, I hope Snow Leopard adoption to live quite rapid. Software that will flee only on Snow Leopard may live here before you know it.

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

    As for the future, it's tempting to view Snow Leopard as the "tick" in a modern Intel-style "tick-tock" release strategy for Mac OS X: radical modern 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 sort of plan, but I consider there's a lot to recommend it.

    Snow Leopard is a unique and fine release, unlike any that beget near before it in both scope and intention. At some point, Mac OS X will surely necessity to rate 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 get 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 flee on Ars, dating back to December 1999 and Mac OS X DP2. If you want to jump into the Wayback Machine and note how far Apple has near with Snow Leopard (or just want to bone up on bar no one at all of the vast cat monikers), we've gone through the archives and dug up some of their older Mac OS X articles. ecstatic 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: trial by Water, February 28, 2000
  • Mac OS X Update: Quartz & Aqua, January 17, 2000
  • Mac OS X DP2, December 14, 1999

  • Inside Mac OS X 10.7 Lion: iChat 6 adds Yahoo IM, account integration, web page sharing | killexams.com real questions and Pass4sure dumps



    The next version of Mac OS X will deliver an updated version of iChat capable of logging into Yahoo IM accounts, providing an improved suffer when using multiple accounts, and adding web page sharing in iChat Theater.The fragmented world of IM

    iChat, Apple's bundled instant messenger app that evolved from origins as an smooth chat client to being a video-enabled IM client supporting the open XMPP/Jabber protocol, now adds support for a third IM protocol: Yahoo IM.

    Unlike email, which bar no one at all providers support via common standards, IM has long been partitioned into proprietary solos, with AOL, ICQ, Skype, Yahoo and Microsoft MSN/Live Messenger bar no one at all using their own closed systems for text and video chat (Apple's .Mac/MobileMe service uses AOL's IM server, and AOL provides an SMS gateway that enables iChat users to transmit SMS messages to mobile numbers).

    Yahoo and Microsoft announced a chat-only gateway between their services, as did AOL and ICQ (AOL until recently owned ICQ). In other cases however, anyone who wants to exchange messages with users on different systems must employ a multiprotocol chat client and create part accounts for each service. Alternatively, you can configure your own gateway server or employ an external gateway that logs into your account on another service to schlepp IM messages between the incompatible account types.

    Mac OS X Lion's iChat 6 now adds support Yahoo IM, although the service appears to only support text chats, not Yahoo audio or video chats. Because of the chat gateway between Yahoo and MSN, this should enable iChat users to compass both populations of chat accounts, in addition to existing support for Jabber/Gmail IM and video chat and AOL/ICQ/MobileMe IM and video chat. However, while the Lion iChat client does travail with Yahoo accounts, the gateway between the Yahoo and MSN does not actually seem to work.

    Evolution of iChat

    Starting with iChat AV in 2003, Apple added support for SIP, standards based video chat. The next year, AOL added compatible video chat in its AOL IM client for Windows, allowing Mac and Windows users to video chat using the smooth network.

    Alongside the release of Mac OS X 10.4 Tiger, Apple shipped a modern version of iChat with support for the open XMPP (Extensible Messaging and Presence Protocol, originally named Jabber), enabling iChat to travail with both smooth and open clients including Apple's own iChat Server in Mac OS X Server and later, Google's GTalk service. iChat's Bonjour chat among local users on the very network besides uses XMPP.

    In Mac OS X 10.5 Leopard, Apple integrated support for VNC screen sharing, allowing users to share their desktop remotely as a video chat over either the XMPP or smooth protocols. Apple besides released iChat Theater, which could share a photo, video, or any document supported by Quick eye over a video chat (below).

    Third party support for tapping into these features was besides added to a modern Instant Message framework.

    On page 2 of 2: modern in iChat 6, iChat vs FaceTime.

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