Apple has announced four new iMacs, all boasting quad-core Sandy Bridge processors and high speed Thunderbolt technology.

According to the company, the new iMacs are up to 70 percent faster than their predecessors with three times the graphics capabilities. There has been little change to the design of the new iMacs though, as they still feature the familiar aluminum and glass design, and LED-backlit high resolution display.

Two of the new models have 27in screens - both come with 4GB of RAM, a 1TB hard drive and quad-core Sandy Bridge processors running at 2.7GHz and 3.1GHz respectively.

There are also two new 21.5in iMacs, which have either a 2.5GHz or a 2.7GHz quad-core Sandy Bridge processor, 4GB RAM and either a 500GB or 1TB hard drive.

The miniDisplay port has been swapped with a Thunderbolt port. The 21.5in models have one Thunderbolt port and the 27in versions two. Apple first introduced the high-speed data transfer Thunderbolt ports in its MacBook Pro refresh, though the technology behind it comes from Intel. Thunderbolt can achieve transfer speeds of up to 10GB per second.

All of the new models include a FaceTime HD camera and FaceTime software built in for video calling. Graphics have also been give a boost with the presence of AMD Radeon HD graphics cards. The 21.5-inch iMacs have a 1,920x1,080 resolution. The 27-inch iMacs have a resolution of 2,560x1,440.

"Our customers love the iMac’s aluminum enclosure, gorgeous display and all-in-one design," said Philip Schiller, Apple’s senior vice president of Worldwide Product Marketing.

"With next generation quad-core processors, powerful new graphics, Thunderbolt technology and a FaceTime HD camera, we've made the world’s best desktop even better," he continued.

The 21.5-inch iMac is available in two configurations: one with a 2.5 GHz quad-core Intel Core i5, AMD Radeon HD 6750M and 500GB hard drive for a suggested retail price of £999.00 inc VAT (£832.50 ex VAT); and one with a 2.7 GHz quad-core Intel Core i5, AMD Radeon HD 6770M and 1TB hard drive for a suggested retail price of £1249.00 inc VAT (£1040.83 ex VAT).

The new 27-inch iMac is available in two models: one with a 2.7 GHz quad-core Intel Core i5, AMD Radeon HD 6770M and 1TB hard drive for a suggested retail price of £1399.00 inc VAT (£1165.83 ex VAT); and one with a 3.1 GHz quad-core Intel Core i5, AMD Radeon HD 6970M and 1TB hard drive for a suggested retail price of £1649.00 inc VAT (£1374.17 ex VAT).

Configure-to-order options include faster Intel Core i7 processors up to 3.4 GHz, additional hard drive capacity up to 2TB, a 256GB solid state drive, additional DDR3 memory and AppleCare Protection Plan. All models are available for shipping within 24 hours, according to the Apple Store website.