Here's a great article on how Hybrid drives work. SSD's are great -- but you pay for the 2-5x faster access time. SSDs still cost almost $1/GB. Hard-drives cost a fraction of this amount. Hybrid drives try to achieve the speed of SSDs, but also keep costs down by using hard-drive materials for the bulk of the storage. How do Hybrids work?
An SSD can read and write data many times faster than the best mechanical hard drive. On the downside, flash memory is many times more expensive than the innards of a typical hard drive, so manufacturers have limited their SSD capacities to hit reasonable price points: A 128GB SSD costs about $130, and for that same price tag, you can buy a 3.5-inch desktop hard drive that delivers 2TB of storage, or a 2.5-inch laptop drive that provides 1TB of storage.
Two years ago, Seagate (quickly followed by Samsung) introduced a drive that married a small SSD with a mechanical drive. The objective was to deliver the superior speed of an expensive SSD, while retaining the higher capacity and lower cost of a conventional hard drive. Now that Toshiba and Western Digital are joining the party, it's a great time to explain in more detail what hybrid drives are and how they operate.
Read more here:
http://www.pcworld.com/article/2012223/hybrid-hard-drives-how-they-work-and-why-they-matter.html
