Two of the biggest hard-disk drive makers, Seagate Technology and Hitachi plan to have terabyte drives on the market within the first half of this year.

Hitachi said it would have a drive available in the retail market before the end of March for $399. Models for use in digital video recorders and enterprise computer servers will follow in the second quarter when production volumes increase, said Doug Pickford, Hitachi's director of market and product strategy.

The 7K1000 drive, which will be on show at next week's Consumer Electronics Show in Las Vegas, will have five 3.5-inch disk platters on which to store data. It will carry a SATA interface on the retail version. A model with the older PATA interface will follow later, said Pickford. It will have a rotational speed of 7,200 rpm.

Seagate said that it planned to begin shipping a 1TB drive sometime during the first half of 2007 to major customers like system and PC vendors during that time-frame. It didn't provide any other details of the drive or its cost. Seagate also didn't address the retail market in its statement.

Terabyte drives, for long a goal of the storage industry, started to get within reach in the last year as drive makers began using a new technology called perpendicular recording.

Like the longitudinal recording that has been used until recently, perpendicular recording relies on magnetically charged particles for data storage. In longitudinal drives, the north and south poles of the magnetic particles run parallel to the disk, but in the new method they are arranged perpendicular to the disk. The result of this new arrangement is that each particle occupies a smaller area of the disk's surface and so more particles can be crammed onto the disk.

The new Hitachi drive will cram 148Gbits of data into each square inch of disk space. In comparison, the company's current highest-capacity 3.5-inch drive, a 500GB model based on longitudinal recording, can only manage half that density.