This customised 27-inch iMac has a powerful 3.4GHz Core i7 processor, one of Intel's new Ivy Bridge chips. At times of high needs, its Turbo Boost feature can reallocate unused resources to temporarily increase its clock speed to up to 3.9GHz.

It also has a Hyper Threading feature, which enables two threads to run on each of its four cores, giving eight virtual cores.

This powerful processor and the 1TB Fusion Drive give the new iMac a huge advantage in our Xbench test, which rates the CPU and storage. It performs over twice as well as the 27-inch 3.4GHz quad core Intel Core i7 iMac from mid-2011.

Its new Ivy Bridge processor proved its worth in our Cinebench tests too, giving an 8.4% increase over last year's similar model.

With Apple's Fusion Drive, you no longer have to choose between a hard disk drive that gives plenty of storage space for your money but is slower than solid state storage, or a speedy SSD that has a massive performance advantage but a much higher price per GB.

A Fusion drive gives the best of both worlds. By storing the operating system on the 128GB flash section, it boots up to 70% faster.

In our tests, a clean install of Mountain Lion took around 20 seconds to boot, an excellent time. Regularly used apps and files are also stored on the solid state section, and moved back to the hard drive if usage falls, to be replaced by more frequently accessed data.

Unlike the 21.5-inch iMacs, which are limited to a 1TB Fusion Drive, you can opt for a 3TB version for the 27-inch models. A word of warning, though. For some reason, you can't install Windows through Boot Camp on a 3TB Fusion Drive.

The new screen technology is amazing. In a reasonably sympathetically lit room, there are hardly any distracting reflections. As a result, on-screen images look more lively and vivid - you could almost reach out and touch them. Colours are very rich too, with glowing primary shades and deep, solid blacks.

The 2012 iMac's 8GB of memory is double the 4GB we got with the last generation. The 27-inch version can take up to 32GB, and unlike the 21.5-inch models, you can install your own at home - there's an access hatch in the back of the casing.

The new iMac has had an audio makeover, too. The speakers are louder and omni-directional, producing a much bigger sound stage than you'd think possible from a computer's internal drivers. Adding external speakers is still an option, but if you choose not to, you're no longer limited to tinny audio. Dual mics with beam forming technology do much to cut down background noise when making FaceTime calls.