Solid state disks are still quite expensive compared to magnetic hard disk drives. You can get a 3TB hard drive with spinning platters for under £90 while a 512GB SSD costs around £250.
A few years ago, Seagate debuted a new promising range of hybrid disks that combines a small SSD memory cache with a traditional hard disk drive. This became the Momentus XT series and its 750GB/8GB model (the Momentus XT ST750LX003) is on sale at Pixmania for £83.40, a saving of £27 off its suggested retail price.
The device comes with two year warranty and uses what Seagate coined its Adaptive Memory technology, making it three times faster than a traditional hard disk drive and operates at hardware level, which means that it is transparent to the OS.
Note that the Momentus XT comes with 32MB buffer, has a 2.5in form factor and is SATA-600.
Most entry level Ultrabooks already use a similar sort of arrangement with an Note that the Momentus XT comes with 32MB buffer, has a 2.5in form factor and is SATA-600. SSD system drive and a bigger magnetic hard disk (usually 32GB SSD and 500GB HDD).
It will be interesting to see whether other manufacturers will embark on the production of similar hybrid storage devices.