Like chocolate and peanut butter, computer hard disk drives and solid state drives are two great tastes that taste great together -- or so hope Western Digital (NASDAQ:WDC) and SanDisk (UNKNOWN:SNDK.DL).

On Tuesday, two of the biggest names in HDDs and SSDs, respectively, announced that they are teaming up to develop a new kind of "hybrid storage device" incorporating both HDD and SDD technology. To build the new device, dubbed the "WD Black solid state hybrid drive (SSHD)," SanDisk will add a SanDisk iSSD storage device to a Western Digital hard disk.

The result, explained SanDisk Senior Vice President Kevin Conley, will be a device with "outstanding hard drive-like capacity, and the slim form factor and the level of performance that you will only get with flash memory solutions." It will have faster speed than an ordinary HDD, plus "instant-on and faster application launching" features.

Specs-wise, the companies say that the WD Black offers 500GB of capacity but will be only half the size of current standard hard drives for notebook computers.

Investors applauded the collaboration, bidding up Western Digital shares by more than 1.2% yesterday, and SanDisk shares by 1.5%. In today's trading, WD shares moved upwards, while SanDisk gave back some of its gains.