The flash memory eliminates the need to spin up the hard disk drive and this could reduce power usage by 10 percent. But it will also prevent problems that occur when the drive is moved while in use.
When the flash memory is full, the hard disk drive is spun up and the data is written to disk. The prototype contains 128MB of flash memory, Greenberg said. Longhorn will also minimize reading from the hard disk drive by storing more data, including application data, in main memory, he said.The company said that it plans to launch these hard drives in late 2006, the same time as Longhorn.
More info at ComputerWorld