Snow Leopard is a bold move. When Apple lifted the lid on the next version of OS X, it promised few new features, but a radical overhaul "refining 90% of the more-than 1,000 projects in Mac OS X."

Three months later it arrived, to inevitable cries of "it's just a service pack!" from Apple's detractors. But do they have a point? Is Mac OS X 10.6 a phenomenally cheap operating system, or an overpriced service pack that should have been a free download? We put it through its paces to find out.

The first thing we noticed after installing Snow Leopard is the speed increase it offers. We installed the new operating system on four different Macs; an iMac, a MacBook Air, a MacBook Pro and a plain old polycarbonate MacBook.

On each machine everything feels snappier and more polished. We had no real complaints about how fast OS X applications such as Mail, iCal and Address Book opened before, but now they appear almost instantly. Your iPhoto picture collection and iTunes album covers appear much quicker too, instead of blinking in one by one.

The difference may be a matter of seconds rather than minutes, but it's amazing how much difference it makes to your day-to-day computing experience. And the speed increase isn't limited to opening applications.

The Finder has been completely rewritten using Apple's Cocoa programming environment, and takes advantage of Snow Leopard's new technologies, such as 64-bit support. Whether it's as a direct result of this or not, we don't know, but even windows containing thousands of items appear quickly and scroll smoothly.

64-bit support

64-BIT SUPPORT: Most system applications have been rebuilt or recompiled in 64-bit

Networks enjoy a speed boost too, with everything being much crisper and more responsive. Starting up your Mac, shutting down again and waking from a sleeping state are all faster than before. For example, our MacBook started up in half the time it did under Leopard, and shut down around 25% faster too. These improvements all greatly enhance the overall user experience.

Power out

System-wide optimisation and dropping support for PowerPC Macs has facilitated a much smaller footprint for Snow Leopard and its bundled applications; installing the new operating system actually saves you disc space.

For example, Mail is reduced from 289MB to 77.5MB, with Address Book tumbling from 55.3MB to 18.6MB, and iChat, Preview and Safari 4 are all around half as spacehungry as before.

According to Apple, installing Snow Leopard saves an average of 7GB hard drive space, but when upgrading a well-used Mac it could save even more. Our MacBook's hard drive finished up more than 14GB lighter. Doing a clean install on the iMac, we saved 17GB.

However, bear in mind that with Snow Leopard, Apple has changed the way it calculates drive capacities, switching from a binary to a decimal system favoured by hard drive manufacturers, which slightly inflates the space saving. (Note that in our examples above, the first figure is in base two, while the latter is in base 10; for an apples-with-apples comparison, the post–Snow-Leopard install figure should be increased a little.)

Despite the potential for confusion, a more compact OS is still very welcome. While Apple isn't making a song and dance about Snow Leopard's new features, you might be pleasantly surprised by what it does offer.