Apple has given its iMac range of desktop computers an overhaul, and most of the changes are aesthetic. The gloss white finish that has made the iMac products almost iconic has been replaced with a stunning brushed aluminium and black design and the casing is notably thinner.

The latest iMac retains the basic form of its predecessor, with the major changes in design coming in both the size, and the materials of the casing. The most obvious change is the brushed aluminium finish, complete with a gloss black bezel and Apple logo. Where the previous model's display was indented into the casing, the new iMac display is completely flush. While the display is bright and clear, it is also rather reflective which may be a turn off to some as it can become distracting, especially in fluorescent lighting. The display also suffered from horizontal colour shift at around 170 degrees but this is in keeping with the standard viewing angle for most monitors and isn't really an issue. Like all of these models, the iMac is welcome news for those who have little desk space. Minimal cables, an integrated silver stand and an almost invisible DVD drive only further enhance its functionality. Ease-of-setup is admirable as all you have to do is unpack the box, plug in the power, keyboard and mouse and you're ready to go.

The other major design change is an all-new aluminium keyboard, which has replaced the previous "crumb catcher". The Wired Keyboard's aluminium aesthetic blends perfectly with the iMac's casing, although we would have liked to see black keys instead of white. The same goes for the included Mighty Mouse - it doesn't really match the new colour scheme of these machines.

Being an all-in-one system, the iMac once again has expandability issues. Only the RAM can be upgraded (there is a single slot for DDR2 memory), located behind a door at the bottom of the screen. The slot can accept 512MB, 1GB or 2GB of RAM with the iMac now supporting a maximum of 4GB RAM in total.

Under the hood there's a 2.40GHz Intel Core 2 Duo processor, 1GB RAM, a 320GB hard drive, an ATI Radeon HD 2600 Pro graphics processor, and a slot-loading DVD SuperDrive. Performance is notable; we managed to run multiple programs including the taxing Adobe Photoshop and didn't notice any real slow down. For casual use, such as web browsing, uploading photos from your digital camera, and playing other media, the iMac performs exceptionally well. The rear casing gets quite hot, although Apple insists this is natural with the aluminium finish.

The iMac ships with Mac OS X Tiger, as well as the latest iLife 08 software - consisting of iPhoto, iMovie, iWeb and GarageBand. We'd advise to wait a couple of months before purchasing this new machine though, as Apple's new Leopard OS is due out shortly, and will ship with the new iMacs as soon as its released.

The Front Row software remains an excellent media feature of the iMac and there is once again an included wireless remote. Unfortunately, some of the same issues remain. The music menu allows you to shuffle songs but only those in your library which means there is no way to shuffle by artist or album. Using the photos menu to share images with family and friends is a worthwhile feature, but Front Row doesn't integrate with some iPhoto slideshow settings such as picture and transition effects. Finally, fast forwarding through movies or videos is a frustrating process as holding down the forward button is simply too slow. We would have liked an option to fast forward videos in increments or at different speeds.

The new iMac once again includes a built-in iSight video camera, housed above the screen at the top of the casing which blends in with the black bezel. A tiny green LED lets you know the camera is switched on when the photo booth software is launched. The microphone is also rather discrete, hidden beneath tiny holes on the top of the iMac's casing. However, this means that the iSight camera can't be rotated or moved, so you'll have to be in front of the computer to capture photos or video.

For connectivity, the new iMac features Bluetooth 2.0, AirPort Extreme wireless networking (802.11n/a/b/g) and a Gigabit Ethernet port. The rear casing houses one FireWire 400 port, one FireWire 800 port, three USB 2.0 ports (as well an additional two on the keyboard), an optical digital audio output and audio line in.

In total, there are four models in the new iMac range. The base 20in model (2.0GHz) comes in at $1698, and the same sized 2.4GHz model (reviewed here) at $2149. There are also two 24in models - 2.4GHz ($2599) and the top of the line 2.8GHz ($3399). The latter comes standard with 2GB memory and a 500GB hard drive.