Apple's latest update to its all-in-one iMacs refines rather than reinvents the classic desktop design, but the changes are still considerable. The 27in iMac sits at the top of the range and, while its new 16:9 widescreen display might make it a bit too ostentatious for some desktops, designers (and anyone else looking for a vast expanse of screen space) will welcome its 2,560 x 1,440 resolution.

The squatter aspect ratio means that the 27in iMac is no taller than the outgoing 24in model, and the overall shape is much the same, although the whole enclosure is now made from a single slab of aluminium for a similar 'unibody' feel as the MacBook Pro.

Another MacBook Pro design touch is the glass screen that extends right to the edge of the case for a frameless front-end. The 'chin' that sits below has also shrunk, and the new iMacs look more like mere monitors than complete computers than ever before.

All iMac screens are now LED backlit, and this technology is both whiter and brighter than the old CCFL displays. It can be set to a much lower brightness level than the old iMac screens too, making these new models much more comfortable to use in dimly lit environments.

The new screens are also thinner and run cooler than those of the old iMacs and, rather than reduce the depth of the case, Apple has used the extra space to fit a big enough cooling system to cope with Intel desktop processors. The switch from mobile chips has little impact on performance (of which more in a moment), but bigger, slower-spinning fans mean less noise when the iMac is under load.

One other minor benefit is that the new iMacs also have room for four memory module slots, which not only means that there's now a 16GB RAM limit, but that inexpensive 2GB SODIMMs can be used for an 8GB configuration. The old two-slot iMacs can only use costly 4GB modules.

Core 2 Duo processors running at 3.06GHz are now standard for all iMacs. This was an additional built-to-order expense on the old models. Despite being a desktop (Intel E7600) chip, this offers no real edge over an old iMac with a same-speed mobile processor, but a stock 4GB of RAM and beefier graphics does provide more bang for much the same buck as before.

Apple is also offering the 27in iMac with Intel's Core i5 or Core i7 processor. Available in November, prices start at £1,599 for the 2.66GHz model, which should offer similar workstation-level performance to the £1,899 Mac Pro and a similar display to the £1,173 30in Cinema Display. That's quite a saving.

One final note: all iMacs now ship with Apple's new Magic Mouse as standard and you can see what we think of that in our separate review coming soon.