The drives, equivalent to about one-fifth of an inch thick with a 2.5-in. form factor, feature hybrid technology, which combines spinning disk with NAND flash.

WD said it developed the new hybrid drive so it would be slim enough for integration into today's thinnest notebook PCs, which feature Instant-On and application performance similar to today's client solid state drives (SSDs).

The new hybrid technology will be showcased during WD's Investor Day, taking place this Thursday.

The new hybrid drive is aimed at notebooks using Intel's Ultrabook specifications. These specifications include Ultrabook Responsiveness Requirements, which set a higher level of performance than a notebook with a hard drive can offer.

In order to achieve higher performance, Ultrabooks must either have two drive bays, one for a hard disk drive and the other for a low-capacity solid-state drive (SSD) cache drive, or a single bay for a hybrid drive.