Apple has begun offering customers ordering the entry-level 21.5in iMac the option to upgrade to the new Fusion Drive, a build-to-order feature only previously available for high-end versions and the 27in iMacs.

First spotted by French blog MacGeneration, the Online Apple Store now gives customers new build-to-order options when purchasing a 21.5in 2.7GHz iMac, allowing them to add a 1TB hybrid Fusion Drive for an additional £200.

Since their launch in October, the 21.5in 2.9GHz iMac and the 27in models of the iMac have been compatible for the 1TB Fusion Drive option, and a £320 3TB Fusion Drive upgrade is available for the 27in models only.

Apple's new Fusion Drive is a hybrid drive that merges a 128GB flash drive with a hard drive – all into a single volume.

Our tests of the iMac (and also the Mac mini) with the Fusion Drive have shown that the new technology can give the computers a big speed and performance boost, but not everyone loves them as much as us.

A blog on MacTrast suggests that Apple's Fusion Drive is an "extremely devious scheme" because Apple has combined it with its proprietary SSD connector, which means consumers can't buy less expensive third-party SSD drives.

Check out our review of the new Apple iMac here.

See also:

Apple iMac 21.5in model unboxed

New iMac 2012 review round-up: what the critics say

New 2013 iMac could ship next spring

Upgrading RAM on new 21.5in iMac 2012 practically impossible

New Mac Pro release date, rumours and leaked images