Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!husc6!rutgers!ucla-cs!zen!ucbvax!decvax!decwrl!pyramid!prls!weaver From: weaver@prls.UUCP (Michael Gordon Weaver) Newsgroups: comp.arch Subject: Re: Disk Striping (description and references) plus class brief Message-ID: <5557@prls.UUCP> Date: Thu, 13-Aug-87 16:36:00 EDT Article-I.D.: prls.5557 Posted: Thu Aug 13 16:36:00 1987 Date-Received: Sat, 15-Aug-87 11:53:41 EDT References: <2432@ames.arpa> <3721@well.UUCP> <2838@phri.UUCP> <155@dolphy.UUCP> <2494@ames.arpa> Reply-To: weaver@prls.UUCP (Michael Gordon Weaver) Organization: Signetics Microprocessor Division Lines: 66 About vacuum disk drives (warning: long winded). As someone who has worked in a disk design lab (albeit as an aide), I had to reply about the idea of vacuum disk drives. Magnetic disks have had flying heads since day one (c. 1954). For the first few years, the heads had air bearings, that is air was forced down through holes in the head to keep the head off the disk platter. Since the sixties (not sure about the date), heads have flown on the air carried along with the platter. Although the platter surface is quite smooth, it is not very flat from the head's point of view: the height difference as the head moves around one rotation is much, much greater than the gap between the head and the platter. The small gap is required for high bit densities. The name winchester comes from the IBM model 3030 DASD (disk), code named Winchester because the number sounded like the nickname of the shotgun manufactured by Winchester company. This drive was (I believe) the first to use 'self-loading' heads, which sat on the disk surface when at rest. Previous disks required that the heads be unloaded from the surface whenever the disk was not up to its full speed, thus requiring a more complicated carriage for the head assembly (comb). The name winchester was latter applied to all disks with self-loading heads, and even latter to all hard disks used in microcomputers. Disk drives in a vacuum would require very flat disks, and some way of keeping the heads at a precise distance from the platter. Also, the head-disk assembly would have to be gas tight and strong enough to withstand full atmospheric pressure. Finally, the type of bearings used for the spindle would probably leak lubricant into the vacuum, so they would have to be changed. Disk drive transfer rates are what they are for a number of reasons, but one of the biggest is standardization. Most drive interfaces will only work with one transfer rate, so disks are engineered with one transfer rate in mind. Generally, total storage size is the most important characteristic for most customers, with head seek time being second, and transfer rate being third. If higher transfer rates were required by a large part of the market, the rotation speed of the drives could be increased from the current typical 3600 rpm to say 10,000 rpm. This would be expensive, but much cheaper than using a vacuum. Computers below about 1 MIPS do not have sufficient memory bandwidth to deal with tranfer rates above the 8 or 16 mega-bits per second rates most popular today. High transfer rates requires otherwise unnecessary costs for low performance machines, and so the market for higher transfer rates is limited. Disk controllers for the current transfer rates can be made of TTL and bitslice (both work up to about 20 mega-bits per second). Going to a higher rate will increase the cost of these. Supercomputer manufactuers and users cannot afford to develop their own disks, since they do not have the volume of sales to divide the development costs over. So they use stock drives, even though they could support higher transfer rates. -- Michael Gordon Weaver Usenet: ...pyramid!prls!weaver Signetics Microprocessor Division 811 East Arques Avenue Sunnyvale, California USA 94088-3409 Phone: (408) 991-3450