Nick Sundby of Hitatchi speaking at the Dataquest Invitational Computer Conference gave an update on the progress of the Digital Video Disk (DVD) consortium. Current CD-ROMs operate at what is termed a constant linear velocity (CLV), with the drive speeding up as the head moves towards the inner tracks, and the fastest drives available today (12x and up) are being spun at rates which were never dreamed up when the physical specification for the CD itself was laid down. Speeds of more than 6000 rpm are required to read the inner tracks of a 12x CR-ROM causing excessive vibration and noise due to minor irregularities in the disk itself. One can imagine a disaster movie type scenario with CD drives spewing out their lethal disks like Odd Job's bowler in Goldfinger! Looking down at the drive in my floor standing mini-tower, I realize that it is placed at a such a height as to cause a long and very painful death. A half way house to true DVD is announced by Hitatchi for its 16x drives. This is termed Partial Constant Angular Velocity. Here the spin speed is adjusted to the head radius up to a certain maximum (CLV), and from then on the drive operates at a Constant Angular Velocity (CAV). Average access time for the 16x drive is given as 90ms. Further optimization can be achieved in software by placing sequential files on the outside edge of the disk for fastest transfer, while random seek files are placed near the center for shortest seek.
True DVD
The true DVD drives are due for shipment to OEMs by mid 1997. These will use completely CAV and have a much smaller pit size. Capacity of the first generation of the new drives will be 4.7 Gigabytes, but this will be pushed up to 17GB by using two sides of each disk, and by having two superimposed layers of data. Recording quality is forecast as being "of near D1 studio" quality. The DVD drives will be backwards compatible with CD-ROM, but not with CR-R (recordable), because of the different laser wavelengths used in the CD-R. Quick on the heels of the DVD will be the DVD-RAM, i.e. a rewriteable device. Sample DVD-RAM devices will be shipping by the end of 1997, with an initial capacity of 2.6 GB. As with today's CD-ROM's the Achilles heel of this technology is the transfer rate. A "mere" 3Mbytes/sec will limit their use in E&P, although this will evolve as the industry seeks out markets other than video.
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