Apple senior vice president of worldwide marketing Phil Schiller described the drive as faster both when reading and writing data than traditional hard drives: You get the speed of a solid-state drive and long-term storage caching on the cheaper, more affordable hard drive part.

Schiller explained that Mountain Lion and the apps that ship with your Mac--like iTunes and iPhoto--reside on the flash drive; other data you add fills up the traditional hard drive. But the Fusion Drive is smart and handles data storage automatically: If you use Numbers more then iMovie, for example, it will automatically move Numbers to the flash side, with iMovie moving to the traditional drive side. Mac OS X figures out what programs you use the most and what would benefit from being on Flash.

Exact pricing for the new iMac with the Apple Fusion Drive installed is not yet available; Apple says that Fusion Drive upgrades will be available in 1TB for the 21.5-inch iMac, and 1TB or 3TB capacities for the 27-inch iMac. The 21.5-inch iMac starts at $1299 and will begin shipping in November. The 27-inch iMac starts at $1799 and begins shipping in December.

Apple offers a $250 1TB Fusion Drive upgrade for the $799 2.3GHz Core i7 Mac mini. Pricing for the Mac mini starts at $599 for the 2.5GHz dual-core i5 version with 4GB of RAM and a 500GB HDD.