Apple’s Fusion Drive Apple is available as a build-to-order option for the 21.5-inch, 2.7GHz 21.5-inch iMac model. Previously, it was only offered for the high-end 21.5-inchers and the 27-inch iMac.
Apple says the Fusion Drive gives customers the performance of flash storage and the capacity of a hard drive. It combines 128GB of flash with a standard 1TB or 3TB hard drive to create a single storage volume that intelligently manages files to optimize read and write performance. Apple says the Fusion Drive adapts to the way you use your iMac and automatically moves the files and apps you use most often to flash storage to enable faster performance and quicker access.