Western Digital today began shipping the world's first 5mm thick hard drives, which the company says will enable new levels of portability in Ultrabooks without the price premium that SSDs entail. The devices will be marketed under two different series: a 5,400RPM single platter unit carrying the Blue moniker, and a solid-state hybrid counterpart with built-in flash storage sold as part of its Black family of storage products.

Both drives sport the same 2.5-inch form factor but are able to shave an additional 2mm off from the 7-mm offerings on the market today through the use of a tiny edge connector that pairs both power and a SATA interface, as part of what Western Digital calls a "clean sheet approach" when designing the drives.

The 2mm reduction might not seem like much of a difference, but the company says it cuts weight by up to 36 percent compared with a standard 9.5 mm drive and makes it 28% slimmer than 7mm drives.

The Western Digital Blue UltraSlim will initially be available in 500 GB capacities for $89.99 through select distributors and  in systems built by OEMs with a two-year warranty.

Pricing and warranty information isn't available for the hybrids, nor are details about the amount of storage and flash cache they will offer. But The Tech Report says they were able to verify some of the missing information, suggesting they will sport MLC NAND capacities between 8GB and 24GB, and launch in two different versions: one with "WD proprietary" hybrid tech, and another based on "industry standard SATA I/O technology."