Seagate Technology has started shipping disk drives that use perpendicular data recording.

Perpendicular recording (PR) achieves its greater density by laying down data bits or domains with the North-South magnetic axis running perpendicularly to the platter. Until now, all the production drives shipped since IBM sold the first disk drives half a century ago have involved longitudinal recording, in which each bit’s magnetic axis is in the same plane as the disk or platter, so taking up more surface space.

According to Seagate, longitudinal recording has run out of steam. Historically, areal density has more than doubled every year, but that rate has dropped to about 40% recently, and the returns will continue to diminish.

Seagate’s new drives are 160GB 2.5 inch notebook devices, and they pack in 45% more bits per square inch of platter than the company’s equivalent conventional, longitudinal recording drives, at the same price.

Seagate says it has already demonstrated double the PR data density that it is now shipping, and that within three to five years it could be selling 3.5-inch desktop or external array drives holding 2TB of data, and laptop drives holding 500GB. The disk maker will begin shipping 3.5 inch and 1 inch PR drives during 2006.

In December Seagate announced its intention to buy rival disk maker Maxtor, a move that will reduce the number of dominant suppliers in the enterprise disk drive market to just two: Seagate, and Hitachi Ltd’s Global Storage Technologies division.

Maxtor was already developing PR disk drives and Hitachi GST said recently that it has already demonstrated very high PR data densities.

Hitachi expects to make volume shipments of PR drives sometime in 2006, which could put it up to a year behind Seagate. However, as Mesabi Group analyst David Hill has pointed out, Seagate’s time-to-market advantage will be significantly limited by the facts that its PR drive output will be finite, and that notebook, PC, server and array makers will take the same cautious approach to PR as they would to any other new technology.