Without an operating system – Mac OS X, say, or Windows XP – a computer is just a dumb box of chips, and even the most exciting application will have no environment in which to run. And, it's easy to forget that you have a choice of which OS you run.
In fact, as a Mac user, you're uniquely positioned because an Intel Mac is the only computer in the world that can legally run all three major operating systems, Mac OS, Windows and Linux. Indeed, you can, if you like, load all three on the same computer and pick which one you want to load when you switch your Mac on.
Even given that you have the choice, though, why would you ever want to install a different OS? Mac OS X, after all, is phenomenally good, and is, we think, the best OS for most people.
There are a few reasons, and it depends on what alternative OS you're thinking of installing. Stick a copy of Windows XP, Vista or (though its support is currently limited) Windows 7 onto an Intel Mac using the Boot Camp utility included with Mac OS X 10.5 and 10.6, and, boom, you've got a PC. It's a very nice PC, and you can always scurry back to Mac OS X if it all gets too much.
But there's essentially zero difference between a Mac running Windows and a Dell running Windows. If you are forced to use Windows-only apps or services as part of your work, for example, add a copy of Windows to your Mac, and you've transformed it into a PC for 100% compatibility with your colleagues.
Remember too that, with Snow Leopard, you can read from the Mac partition of your hard disk too.
Opting for Linux
But what about Linux? Why would you want to install that OS, (unfairly) perceived as being difficult and nerdy, onto your lovely Mac?
We asked Paul Hudson, the editor of our sister title Linux Format. "The most common reason for people running Linux on their Mac," he said "is simply because they can get a bang up-to-date operating system running just fine on 400MHz PowerPC chips. Linux supports every major computer architecture in the world, you can even use a G3 if you really want to, but make sure you have at least 256MB of RAM.
"Other folks use it because they want a bit more power on their desktop: it's straightforward to set up, comes with tens of thousands of programs that are completely free to use, and is pretty much bulletproof in terms of security. But my favourite reason is simply for the fun of dabbling around – I like to break things and fix them again, and, while Linux does make it hard to shoot yourself in the foot, when you do you'll take your whole leg off."
As Hudson says, these days Linux is fairly easy to use as your primary operating system. It's not quite as robust as OS X when it comes to certain Mac hardware, but to be fair it's almost impossible for any operating system designed to run on more than a small range of computers to be as stable.
Breathe new life into an old machine
Otherwise, Linux is excellent. Don't discount, either, its astonishing abilities to breathe new life into old hardware. If your old G4 is still chugging along with Mac OS 9, wiping the slate clean and installing a nice friendly, modern version of Linux will introduce you to a whole new world, with free, powerful software that's regularly updated.
Even simply being able to use a standards-compliant browser such as Firefox 3 rather than Internet Explorer for Mac is a boon when, today, so much of our lives are or can be carried out online.
Of course, you could put Linux on a brand-new Mac Pro if you like, and indeed, as apart from doing it just for the fun of it, many people run Linux as their primary OS because they applaud the ethos behind the open source movement.
It's not just a whimsical delight in getting software that's free and which has been built by thousands of volunteers all over the world, but a passionate dedication to the idea that data ought not to be locked away in proprietary formats or hamstrung by DRM.
There are, however, many versions of Linux. They're known as 'distros', short for distributions, and you have to decide which to install. We asked Hudson for advice.
"This really depends on what you consider an 'old' Mac to be," he said. "Let me put it like this: if the words 'old world' mean nothing to you, go for Ubuntu; it runs on G3, G4 and G5 (or Intel) CPUs. Ubuntu is by far the most popular Linux distribution, and with good reason: it's easy to use, well polished, and has an active community offering help at ubuntuforums.org.
"Long-term Mac users who have hardware better suited to museums should look at Debian. If you're an advanced user with an Intel Mac, give OpenSUSE a try: it's a 'full-fat' distro, which comes on a DVD and installs pretty much all of it to your hard drive. If you want to try lots of text editors to find one that suits, OpenSUSE is a good place to start."
A learning curve
Even with the simplest of distros there will be a learning curve, though it's much shallower than it was a few years ago. For example, warns Hudson:
"Mac users are quite familiar with downloading .dmg files from the web then dropping programs into their Applications directory. Linux doesn't do things like that, because we have a natural distrust of getting files from random websites. Instead, you'll find your distro uses a package manager, which is where you select the software you want and it downloads and installs it for you from a trusted source. To remove the program, use the package manager again."
Modern Linux distros support common Wi-Fi chipsets, so you may find that Wi-Fi works on your freshly installed Linux box right away. If not, you might have to download some drivers. The good news: distros such as Ubuntu can automatically identify and download appropriate drivers. The bad? They need a network connection to do this.