Although positioned as an under-the-hood upgrade to Leopard, Apple Mac OS X 10.6 Snow Leopard offers a lot of changes on the surfaces as well. UPDATED: 27 August 2009.

Under the hood, Mac OS X 10.6 Snow Leopard offers a 64-bit OS for faster processing and greater memory access, support for multicore processing via Grand Central Dispatch and OpenCL, and faster Java and QuickTime performance. These features, combined with the low upgrade price of £25, make Snow Leopard the biggest no-brainer of an upgrade since Mac OS X 10.1.

Do note that Snow Leopard does away with two old Apple technologies. It no longer supports the long-waning AppleTalk network protocol, and it won't run on PowerPC-based Macs. If you have PowerPC apps (such as the Microsoft Office Update utility), note they will run if you have Apple's Rosetta technology installed. Snow Leopard does not install Rosetta automatically, but you can install it using the Optional Packages installer on the Snow Leopard installation DVD.

If you're not sure whether your computer can run Snow Leopard, click on the Apple menu and check "About This Mac." If your processor is a PowerPC G4 or G5, your Mac cannot be updated with the new OS. Snow Leopard still runs older PowerPC-based applications, but it will not boot a PowerPC-based Mac.

For everyone else with Intel-based hardware, Apple requires 5GB of available disk space, 1GB RAM, and an optical disk drive capable of reading DVDs (or, in the case of the MacBook Air, a DVD drive accessible via Remote Disk).

Installing Mac OS X 10.6 Snow Leopard

Unlike previous editions of Mac OS X, which could be freely installed on any old Mac so long as it met the system requirements, Snow Leopard's licence specifically limits it to users who are already using Leopard, which has been shipping since October 2007.

If you are a Leopard user, you can upgrade a single Mac for £25, or up to five Macs in one household with the Snow Leopard Family Pack for £39.

Users of Tiger - essentially people who bought Intel Macs before Leopard was released and never upgraded - are supposed to purchase the Mac Box Set, which includes Snow Leopard, iLife '09, and iWork '09, for £129.

To compare: Microsoft's Windows 7 Ultimate upgrade costs £199, and the full version is £229 (there's no Family Pack for the Ultimate edition). Why compare Apple's latest with Ultimate? Because on the Windows side, Ultimate is the full-featured version. Snow Leopard comes in just one full-featured version.

Windows 7 review

Apple continues to rely on the honour system for Mac OS X. Not only does Snow Leopard not require the entry of any serial numbers, but the standard version of Snow Leopard is a bootable "full install" disc that doesn't actually check for the presence of Leopard in order to install.

Install Snow Leopard

This also means that if, at a later time, you want to wipe your hard drive and reinstall Snow Leopard, you won't have to first install Leopard and then run a separate Snow Leopard upgrade on top of it.

(It also means that Tiger users could install Snow Leopard directly onto their Macs without first installing Leopard via OS X 10.5 discs or the Mac Box Set. However, this would go against the terms of Apple's Snow Leopard software licence.)

The Snow Leopard installation process is different from previous OS X installers. Rather than requiring an immediate restart, a lot of it takes place as soon as you double-click the installer.

After choosing where to install the new OS, Snow Leopard will copy a large chunk of the data needed for installation from the DVD to your hard drive.

That helps speed up the whole process - Apple says it's 45 percent faster than the old installation routine because the installer reads the data copied to your hard drive rather directly from the DVD.

About halfway through the installation, the Mac reboots and finishes up the task at hand. You may notice that the screen goes dark during the installation. That's because the whole process is automated and you don't have to monitor what's happening. If you move the mouse or touch the trackpad, the screen wakes up and you can see where things stand.

In previous versions of OS X, you had the option of installing drivers for the printers of particular vendors. But Snow Leopard doesn't work that way. Instead, it automatically installs drivers for printers your computer has used in the past. If you're on a network, it installs drivers for the connected printers it finds out there, too. And it installs drivers for printers Apple considers popular.

Because it removes all of the old operating system files - in previous OS X upgrades they used to go into a "Previous System" folder - hundreds of megabytes, if not gigabytes, of space are freed up.

The OS also takes up less room because the Universal code that was built into Tiger and Leopard to run PowerPC Macs is no longer needed, since Snow Leopard is Intel-only. According to Apple, most users will gain back 6GB of space.

If you choose to customize your installation, you'll notice that the installation of printer drivers is entirely different in Snow Leopard. Turns out most of us are wasting gigabytes of hard-drive space on printer drivers that we don't need.

Custom Install Snow Leopard

What happens if you encounter a strange, new printer? If you've got an Internet connection at that moment, you shouldn't have much trouble: Snow Leopard will automatically download and install the drivers it needs.

If you really need bullet-proof, instantaneous compatibility with a vast array of printers, you can opt to install all the drivers - you just won't realize the disk-space savings you might have otherwise.

There are some other notable options in the customized installation window.

Snow Leopard Rosetta

Rosetta, the technology that enables code compiled for PowerPC chips to run on Intel chips, is available - but is not installed by default. Rosetta only takes up a few megabytes of drive space, and without it older programs simply won't run, so if you have such programs, that option is worth checking. To find out if an App is PowerPC only, select an old app and choose Get Info; if its Kind is listed as Application (PowerPC), it needs Rosetta.

Does Adobe CS3 work with Snow Leopard?

Which apps don't work with Snow Leopard?

If you don't, and if you later try to launch a PowerPC app, Snow Leopard will pop up a window to explain that you need Rosetta and offer to install it for you (via Apple's Software Update utility).

Another technology making a surprise appearance in the installation-options list is QuickTime. No, QuickTime hasn't suddenly become optional in Snow Leopard. But Snow Leopard's new QuickTime Player is as radical a departure from the old model as iMovie '08 was from iMovie HD: it's a complete reimagining of the app, one that strips away many features that many of us find useful.

If the Mac you're upgrading to Snow Leopard includes a QuickTime Pro key, you'll find that QuickTime Player 7 is still on your Mac, but has been moved to the /Applications/Utilities folder. If you don't have a QuickTime Pro key but still want access to the classic QuickTime 7 player, you'll need to do a custom install in order to get it.

Snow Leopard Wallpaper

NEXT: Snow Leopard: Look and feel >>

Quick Links:

2. Mac OS X 10.6 Snow Leopard: Look and feel

3. Mac OS X 10.6 Snow Leopard: Speed and stability

4. Mac OS X 10.6 Snow Leopard: Application tweaks

5. Mac OS X 10.6 Snow Leopard: QuickTime Player X

6. Mac OS X 10.6 Snow Leopard: Security

7. Mac OS X 10.6 Snow Leopard: Nice touches

8. Mac OS X 10.6 Snow Leopard: More tweaks

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