Scotts Valley, California-based Seagate Technology Inc and Sony Corp say that Sony’s Pre-Embossed Rigid Magnetic or PERM medium, which they look to to increase capacity and reduce manufacturing costs for disk drives (CI No 2,585), unlike conventional magnetic media, exploits optical technology in that the disks are plastic, not aluminium or glass, and like CD-ROM disks have all the tracks moulded on to them when produced. The two say because the servo tracks are moulded into the plastic substrate, a number of steps normally part of magnetic disks’ manufacture, can be eliminated, chiefly the need for a servo writer. This in turn reduces the cost of manufacture. The technology enables greater track density: Seagate speculates that a 2.5 disk could store almost 1.3Gb. But there is apparently no problem of interference between tracks so closely written. This is because, according to the company, the tracks are put in place so that the fringe field from the edges of the head does not affect the next track. Seagate says between these discrete tracks is a deadband. Such narrow tracks need much finer heads, and these too are being developed by the pair. Another claim being checked in the prototype versions the companies are developing is the signal-to-noise ratio. The pair doubts commercial products would be available much before 1997-98. Problems they say need to be addressed include spinning a plastic disk close enough to a head and how to get the smoothest plastic disk.
