Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!know!samsung!dali.cs.montana.edu!uakari.primate.wisc.edu!aplcen!haven!ncifcrf!lhc!usenet From: usenet@nlm.nih.gov (usenet news poster) Newsgroups: comp.arch Subject: Re: Data Storage density questions Message-ID: <1990Jul31.200043.5189@nlm.nih.gov> Date: 31 Jul 90 20:00:43 GMT References: <2635@mindlink.UUCP> <10048@pt.cs.cmu.edu> <2684@network.ucsd.edu> Reply-To: states@tech.NLM.NIH.GOV (David States) Organization: National Library of Medicine, Bethesda, Md. Lines: 24 In article <2684@network.ucsd.edu> mbk@inls1.ucsd.edu (Matt Kennel) writes: >You mean disk drives are not evacuated? >Wow, you learn something new every day. > >Come to think of it, why not? I should think that it would be nice to >be able to position the head without worrying about such ugly things as the >viscocity of air and its pressure & temperature and the roughness of the >platter. Fluid mechanics is exceedingly tough so why bother when you >don't have to? The key to Winchester and subsequent disks is use of aerodynamics to "fly" the head at a controlled height maintained by the fluid dynamics. No air -> no fluid dynamics -> head crash. While on the subject, why do disks spin so slowly? At 3600 RPM, you have an intrinsic delay of up to 16 msec waiting for the platter to come around, no matter how fast the heads move. You could increase the speed of a 5 1/4" disk by an order of magnitude without worrying about g forces. Aerodynamic heating becomes a problem at higher velocities, but you don't hit the speed of sound until ~120,000 RPM. >Matt Kennel David States