Apple has finally upgraded its smaller 21.5-inch iMac with 4K display technology and a much-needed specs boost, according to Digital Spy.

The new screen is the machine's headline feature, offering a dramatic improvement on its predecessor's 1080p panel, boasting a 25% wider colour range.

The latest iMacs make the jump to Intel Broadwell processors with Iris Pro graphics and 8GB of 1867GHz LPDDR3 RAM, upgradeable to 16GB if that isn't enough for you.

Apple has also refreshed its 27-inch iMacs, with all models bumped up to a 5K display with the same wider colour gamut as the smaller machine.

To accompany the new iMacs, Apple has redesigned its mouse, wireless keyboard and Magic Trackpad, adding built-in batteries that power up via a Lightning cable.

The keyboard is now 13% smaller, but with larger keys, while the Trackpad brings pressure-sensitive Force Touch gestures to desktop.