Two new hard drives have been announced by Toshiba. Designed for ultra-mobile PCs, they are the 120 GB single platter MKxx31GAL series(also available in a smaller, 80 GB size), and most notably the 240 GB MK2431GAH, which is the world’s first dual-platter 240 GB hard drive.

Both measure at just 1.8 inches and weigh up to 2 ounces, and thus could conceivably be used in very small mobile devices such as iPods or other portable media players.

The two devices use parallel ATA interfaces, and have the industry’s highest area density with 344 GB per square inch. This is achieved using the fourth generation of the perpendicular magnetic recording technology introduced by Toshiba themselves back in 2005. The technology allows for three times the storage density compared to traditional longitudinal recording used in HDDs today.

They use 33% less energy than previous models, thus allowing a rotation speed of 4,200 RPM, compared to the 3,600 RPM of other large drives in their class. Another feature designed to increase read/write performance is the drives’ 8MB of cache.

While unlikely to be sold on their own, the new ultra-compact drives are to be shipped by Toshiba for use in CE and mobile devices, camcorders, mobile PCs and other home electronics to be released this holiday season. Toshiba have not named any customers, although clients such as Apple are known for using Toshiba compact hard drives regularly.