Apple has announced that it's new iMacs shipping in November will boost of fusion drives having advantages of both HDD(storage) and SSD(speed).
Intel already has fusion drives which are developed based on Intel smart response technology.
Whats new in iMac's fusion drive?
Intel's fusion drive - uses caching method
iMac's fusion drive - automatically transfers frequently used files from HDD to SSD part of the drive.
And again the Apple has come up with an unique concept and we will have to wait and see whether this approach translates into better speed and lesser power consumption.
Advantages and disadvantages of HDD and SSD : http://www.storagereview.com/ssd_vs_hdd