Along with new iMac and Mac mini models, Apple introduced a new data storage feature on Tuesday called Fusion Drive. The Fusion Drive is a hybrid storage system that combines 128GB of flash-based storage with either a 1TB or 3TB spinning hard drive that Apple says will offer a substantial performance boost compared to using just a traditional hard drive.
According to Apple, "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."
By dynamically moving the apps you use most often to flash storage, Fusion Drive can enhance overall performance since disk intensive tasks are handled by the faster solid-state storage.
Currently, Apple is offering Fusion Drive as a build-to-order option on the just announced Mac mini and 27-inch iMac -- at least on the Mac mini which is available now. The new 27-inch iMac will be available in December.