Apple has revamped its iMac computer range, introducing new models with 20in and 24in screens and launching a new ultra-thin aluminium keyboard.

The new 20in and 24in iMacs offer audio input and output, three USB 2.0 ports, FireWire 400 and 800, Gigabit Ethernet and video out. The slot-loading ‘SuperDrive’ has been retained, along with a built-in iSight webcam and microphone. The displays have the glossy sheen to them as used on the MacBooks.

"This new iMac is the most incredible desktop computer we’ve ever made," said Steve Jobs, Apple’s CEO. "Our new design features the innovative use of materials, including professional-grade aluminium and glass, that are highly recyclable."

In another nod to the environment, the new iMac also meets the stringent Energy Star 4.0 requirements.

There is also a new ultra-thin (0.33in) aluminium keyboard (a wireless version optionally available for £49) confirming rumours of the images shown on the internet. It sports dedicated dimmer, Expose, Dashboard and media keys. Both the wireless keyboard and mouse support Bluetooth 2.0.

Like the Mac Pro, the iMac is now built to order. You can choose an Intel Core 2 Duo processors clocked from to 2.4GHz to 2.8 GHz. They support up to 4GB of RAM, and feature ATI Radeon HD 2400XT graphics. They also feature hard disk drives up to 1TB in capacity, and feature 802.11n wireless.

The new iMac includes the latest Intel Core 2 Duo processors running up to 2.8GHz with 4MB of shared L2 cache and up to 4GB of 667 MHz DDR2 SDRAM memory.

"iMacs have been very successful, and we'd like to make it even better," said Jobs. Apple is borrowing two elements from its Pro products for this new generation of iMac - aluminium and silicon dioxide, better known as glass. Aluminum is extremely durable and very lightweight, and pros love Apple's pro products - the MacBook Pro and the Mac Pro are both made from it. Glass, Jobs explained, is a very elegant material and scratch resistant. It's also recyclable.

Three models are available: an entry-level 2.0GHz 20in iMac ($1,199), a better-specified 2.4GHz 20-inch model ($1,499) and a 24in 2.4GHz model ($1,799).

The entry-level model hosts a 250GB drive, the other offer 320GB drives. The entry-level model carries an ATI Radeon HD 2400 XT graphics card, while the other models offer an ATI Radeon HD 2600 Pro.

The new iMacs ship with iLife ’08. The 20in iMac now starts at just £799 (inc VAT), £200 less than the previous 20in model, and the 24-inch iMac starts at just £1,349 (inc VAT), £200 less than the previous 24in model.