Like its predecessors, this new edition of the Apple iMac is an all-in-one computer, in that it includes the processing unit, DVD writer, webcam, microphone and screen in a single unit.

The 2009 iMac features an almost identical aluminium body to last year’s model, the only obvious external changes being a slightly tapered base, an extra USB port instead of the Firewire socket and a Mini Displayport socket instead of the Mini DVI one.

Unfortunately, the mouse is still the old white one, at odds with the black and aluminium elsewhere in the iMac's design. The included aluminium keyboard, on the other hand, has been changed. The numeric keypad has been completely removed, making it a compact and slim device. Users preferring a keyboard with a keypad can opt for a full-size keyboard at the time of ordering for no extra cost. As both keyboard and mouse are USB-connected, it is a simple matter to substitute them for equivalents if you'd prefer others.

Despite a clear, bright, high-resolution screen, the 20in iMac is only available with a glossy glass-finished screen. Still, we encountered no problems with stray reflections when using the unit under fairly harsh lighting or bright sunlight.

Like all Apple computers, the iMac doesn't use Windows – rather it uses the Apple Mac OSX operating system. It’s slick, fast and stable, and Apple make much of usability and being as intuitive as possible. Perhaps the most important thing about Mac OS for home users is the included iLife 09 suite of applications. These make photo organisation, web design and movie and soundtrack making easy – certainly as much as any paid-for programs we have seen.

The specifications of the 20in iMac have been beefed up too: the main processor is still an Intel Core 2 Duo, it's now a quicker variant. The memory has been doubled to 2GB and there is a larger 320GB hard disk, while the graphics card has also been updated to an Nvidia 9400M.

It's not exactly good news all round, though, as this bottom-of-the-range model costs £949, as opposed to last year’s entry-level model that cost only £799.

Despite the specification increases and given the inflated price, there is little obvious benefit of the 2009 edition 20in iMac over the cheaper 2008 model at the same screen size, so existing users have no reason to upgrade. Since it's not possible to buy the 2008 model new any more, newcomers don't have much choice.

Those looking to make the switch to Mac from Windows will find the new iMac usable, attractive and powerful, although it's considerably more expensive than we would have expected.