Although SSD prices are falling, hard drives remain cheaper by about a factor of 10. Western Digital expects that delta to persist for the foreseeable future, so it's working on a hybrid solution that combines the two storage types. Due out this year, this Black-branded "SSHD" will pair a solid-state cache with mechanical platters.
WD is demoing the drive at the Consumer Electronics Show in Las Vegas, and Scott got a first-hand look at it. The demo involved loading a suite of applications, and it took 81 seconds on a standard hard drive. An SSD ran the demo in just 51 seconds, while the SSHD completed it in 55 seconds.
Like Seagate's Momentus XT hybrids, WD's SSHD solution uses its flash memory as a read cache. Incoming writes from the host system aren't stored in the NAND, although that may change for future generations. Interestingly, the caching mechanism is controlled by a combination of firmware and host-based software drivers. The Momentus XT's caching is implemented entirely in the firmware, and I'm curious whether bringing the host PC into the picture provides any benefits. We've already seen good results from driver-based caching solutions like Intel's Smart Response Technology, which allows SSDs to be configured as caches for traditional hard drives.
Western Digital's upcoming hybrid will have a 2.5" footprint and a 7-mm thickness, which should allow it to squeeze into thinner notebooks than typical 9.5-mm mechanical offerings. It looks like an even slimmer 5-mm version may be in the cards, as well.