MacRumors report that the new 27-inch iMac released today offers support for dual hard drives: one traditional Serial ATA in 1 TB or 2 TB capacity and one 256 GB solid state drive (SSD)

To give your iMac a real performance boost, configure your 27-inch iMac on the Apple Online Store with an optional 256GB solid-state drive. You can choose it as your only drive or have it installed in addition to the built-in hard drive, allowing you to store the operating system, critical applications, and important files on the solid-state drive and your other files on the hard drive. Because solid-state drives have no moving parts, the computer can access data at over twice the speed of hard drives. Which makes starting up your iMac and launching applications faster than you ever thought possible.

Apple's New 27-Inch iMac Supports Secondary Solid State Hard Drive