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Newsgroups: comp.unix.bsd.netbsd.misc Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!simtel!pravda.aa.msen.com!sdd.hp.com!usc!cs.utexas.edu!convex!news.duke.edu!news.mathworks.com!newsfeed.internetmci.com!EU.net!Germany.EU.net!nntp.gmd.de!nntp.darmstadt.gmd.de!news.th-darmstadt.de!hrz-ws11.hrz.uni-kassel.de!phase23!citylink.dinoex.sub.org!peter From: peter@citylink.dinoex.sub.org (Peter Much) Subject: Re: Translated geometry MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Organization: Buero fuer Sektenforschung und Qualitaetspruefung in der Esoterik Message-ID: <DDA36o.264@citylink.dinoex.sub.org> References: <Pine.SOL.3.91.950810081116.19831A-100000@ritz> <40js8c$gjs@news.ccit.arizona.edu> Date: Mon, 14 Aug 1995 02:06:23 GMT Lines: 27 In article <40js8c$gjs@news.ccit.arizona.edu>, Thomas J. Trebisky <tom@canopus.as.arizona.edu> wrote: >And yes, the reason for translation is brain damage in the BIOS code which >needs to root around on the disk to get you booted. I think the BIOS is >unable to deal with more than 1024 cylinders (for no particular reason that >occurs to me other than that being the limit in the old WD1010 controller >chip that almost all PC's used to use back in the MFM days.) You're right. The reason is, the BIOS code is called via soft-interrupts, with giving the respective data to it in the CPU registers. They have defined only 10 bits for the cylinder nr., and these calls have to be the same for PC-XT 8088 and AT 80286 (and all above). The Bios then hands the data on to the IO-Port, and on AT it's 16 bits there. I didn't hack the XT controller, but on AT i had a Microscience HH1090 MFM drive with 1314 cyls., and i had quite a fun with pre-formatting that. So, the problem isn't new, only the solution. IBM-PC architecture was brain-dead from the beginning. Seems IBM didn't want to make a good PC, but to make money fast. Peter -- Write to: Peter Much * Koelnische Str. 22 * D-34117 Kassel * +49-561-774961 peter@citylink.dinoex.sub.org much@hrz.uni-kassel.de p.much@asco.nev.sub.de