The Tech Report saw a demonstration of a Black-series "SSHD" from Western Digital at CES 2013. This new hybrid device pairs solid state cache with mechanical platters in an attempt to deliver the best from both worlds, you get a significant performance boost from the fast flash memory and the cheap storage capacity of a HDD. In a demo being showcased at CES, the SSHD loaded a suite of applications in 55 seconds, only four seconds worse than an SSD, while a standard hard drive took 81 seconds to finish the test.
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.
The WD SSHD will be offered as a 2.5" disk with a 7mm thickness, making it suitable for ultraportable laptops and ultrabooks. The site also heard that an even slimmer 5mm version may be in the cards, as well.