Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!husc6!cmcl2!phri!roy From: roy@phri.UUCP (Roy Smith) Newsgroups: comp.arch Subject: Re: Disk Striping (description and references) plus class brief Message-ID: <2838@phri.UUCP> Date: Tue, 11-Aug-87 10:17:51 EDT Article-I.D.: phri.2838 Posted: Tue Aug 11 10:17:51 1987 Date-Received: Fri, 14-Aug-87 04:26:39 EDT References: <2432@ames.arpa> <3721@well.UUCP> Reply-To: roy@phri.UUCP (Roy Smith) Organization: Public Health Research Inst. (NY, NY) Lines: 32 Summary: Put disks in a vacuum In article <3721@well.UUCP> rchrd@well.UUCP (Richard Friedman) writes: > there is a real limiting factor to disk technology, and it is not the > speed of light (the limiting factor to CPU technology) but rather the > speed of sound. If you try to make a disk go too fast in an attempt to > improve transfer rates, you approach Mach 1 in the turbulent flow around > the surface of the disk, and the resulting shock wave destroyes the disk, > literally. So, why not put the disk in a vacuum? We've got ultracentrifuges all over the place here that run as fast as 100,000 RPM. Of course, the rotor chamber is kept under hard vacuum with a diffusion pump, and the walls of the chamber have refrigeration coils to carry away the heat caused by the few air molecules remaining, but why couldn't you do that do a disk drive if you wanted to? Ultracentrafuges run at about 50 microns of vacuum; for a 36,000 RPM disk you wouldn't need anywhere near that; a few PSI would probably be fine. We've got 20,000 RPM centrifuges that run in atmosphere, but they don't have delicate read/write heads and oxide surfaces to worry about, and the condensation on the outside of the rotor from the refrigeration doesn't bother them either. I understand that in big power plants, the insides of the generators are filled with hydrogen instead of air because the speed of sound is faster so the rotor tips don't go supersonic. Apparantly, as long as you keep oxygen away, there is no danger of explosion. You could have hydrogen-filled disk drives, I suppose. Sure would make head crashes more exciting! :-) -- Roy Smith, {allegra,cmcl2,philabs}!phri!roy System Administrator, Public Health Research Institute 455 First Avenue, New York, NY 10016