Apple has updated its entire family of iMac desktop computers, introducing its best display technology to each category.

The line-up of 21.5-inch iMacs now includes a model with a 4K Retina display, coming with a pixel resolution of 4096 x 2304. And all 27-inch models now come with a Retina 5K display as standard, sporting a resolution of 5120 x 2880.

Other specifications boosts include faster processors and graphics, two Thunderbolt 2 ports and new storage options.

The 27-inch models now come with 6th generation Intel (Skylake) Core processors and AMD high-performance graphics. The 21.5-inch with Retina 4K display features a 5th generation Intel Core processor and Intel Iris Pro graphics.

And there is now three-stream 802.11ac Wi-Fi on board that is capable of up to 1.3Gbps wireless networking. The Thunderbolt 2 ports are capable of transferring data up to 20Gbps from a supporting external drive.

READ: Apple iMac with Retina 5K display review: Pixel-packed powerhouse

The iMacs are also available with Apple's Fusion Drive technology for storage, which is effectively the company's answer to hybrid drives. They combine conventional hard disk tech with flash storage technology to provide both larger drive space and faster access times.

Fusion Drive is available in 2TB and 3TB configurations, with 128GB of flash.

Another option on offer is a pure flash drice, which is now available at up to 1TB.

Prices for the new models start at £1,199 for the 21.5-inch iMac with Retina 4K display and £1,449 for the entry-level 27-inch iMac with Retina 5K display. The Full HD 21.5-inch iMac starts at £899.

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