Not to be outdone by Hitachi's new 7200rpm, 500GB 2.5in hard drive, rival disk maker Toshiba has announced a 640GB model, though it only spins at 5400rpm.

The full capacity is delivered on just two storage platters thanks to a data density of 528.5Gb per square inch. It means the capacity can be delivered without upping the drive's height beyond 9.5mm.

Toshiba also claimed such a high density makes the product more environmentally friendly: fewer components mean less carbon-dioxide is released during the drive's manufacture, it said.

The drive contains 8MB of buffer memory, and connects across a 3Gb/s Sata bus.

Versions of the drive will also be made available with capacities of 500GB, 320GB, 250GB and 160GB. PC manufacturers will be able to buy the drives in Q4. ®