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Path: sserve!newshost.anu.edu.au!harbinger.cc.monash.edu.au!msuinfo!agate!howland.reston.ans.net!swrinde!emory!cherry.atlanta.com!nntp.mindspring.com!usenet From: rsanders@mindspring.com (Robert Sanders) Newsgroups: comp.os.386bsd.development Subject: Re: users - not entirely clear on the concept Date: 12 Jun 1994 22:35:00 GMT Organization: MindSpring Enterprises, Inc. Lines: 35 Message-ID: <RSANDERS.94Jun12183500@hrothgar.mindspring.com> References: <Cr8EBv.BDM@hippo.ru.ac.za> <2t7beb$p0n@menudo.uh.edu> <2tamoa$22 <2tdcdo$58u@news.ysu.edu> <2tf7l7$2jk@s069.infonet.net> NNTP-Posting-Host: msdem5.mindspring.com In-reply-to: burgess@s069.infonet.net's message of 12 Jun 1994 09:55:35 -0500 Linux's way of dealing with the problem (allowing the BIOS to be active, or something like that) is probably good for Linux; from what I recall of the great "I'd give you an F" debate in comp.os.minix, the reason is to avoid the specific problem that we have caused ourselves in BSD. It has its costs, but it works. Linux simply asks the BIOS at boottime (while still in 16-bit real mode) for the disk geometry, and then believes it. It isn't so difficult, really. There are a few drawbacks to this as well, but I don't think they're problems as large or common as the ones that BSD users have: 1) You have to be able to wedge the geometry into the BIOS table. For users of large drives, this may not be possible or very efficient. 2) You may get a "false" geometry. This prevents you from doing some gemoetry-based optimizations like UFS does, but then again with modern drives the true geometry isn't as simply as a c/h/s count anyway. 3) Some machines, like PS/2s, don't work with the standard BIOS query. 4) For machines with >2 IDE drives (on a second, hacked controller), you have to compile in the geometry of the disks or specify it at boottime as a kernel option. The advantages are that Linux's idea of the disk geometry is probably more in line with what other operating systems (like DOS) think, allowing them to coexist without trouble. A system that uses both approaches -- BIOS as well as the IDE get geometry command -- would probably be ideal.