With the introduction of all new 2012 iMac & updated Mac Mini, Apple has also debuted a new “Fusion Drive” that combines the benefits of a Flash SSD and a traditional hard disk drive. It comes in two options i.e a 128GB SSD combined with 1TB HDD and 128GB SSD combined with 3TB HDD.
According to Apple, the Fusion Drive performs on par with a standard SSD. The drive manages everything in the background and as you use the computer it learns what you use the most and moves those apps to the SSD to increase performance.
Fusion Drive is an innovative new storage option that 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. 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.
The Fusion Drive works automatically with OS X Mountain Lion.