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From: cechew@bruce.cs.monash.OZ.AU (Earl Chew)
Newsgroups: comp.os.minix
Subject: Re: Minix & Hardcards
Message-ID: <3451@bruce.cs.monash.OZ.AU>
Date: 11 Dec 90 03:22:23 GMT
References: <38601@nigel.ee.udel.edu>
Organization: Monash Uni. Computer Science, Australia
Lines: 49

In <38601@nigel.ee.udel.edu> Peter_Van_Epp@cc.sfu.ca writes:

>The way I always figure out the geometry of the disk (and I just got a new
>200 M drive and a 386 machine!) is to let the disk bios tell me from DOS.
>All you need is a 5 line program under debug (assuming of course that you
>have MSDOS!) that looks like this
>a 100
>mov ah,8
>mov dl,80
>int 13
>nop
>nop

More user friendly ways along the same lines are to use something like Norton's
NU, or infoplus (posted recently to comp.binaries.ibm.pc). These will tell you
the disk geometry in nice bright friendly letters.

This is well and good, but can lead to *wrong* results. All these schemes rely
on the BIOS to tell you what's what. In particular, on new AT machines, what
the BIOS thinks you have installed is what you tell it (using SETUP, or boot
time configuration using one of the fancy new BIOSs). For example, if I have
a 7 head, 872 cylinder and 17 sector disk, I could use SETUP (or its
equivalent) to tell the BIOS that I have a 4 head, 400 cylinder, 17 sector disk.

Then Norton NU, infoplus or the debug technique described here will report a
4 head, 400 cylinder, 17 sector disk. Alternatively, if I setup the BIOS to
think that I have a 16 head, 1024 cylinder, 26 sector disk, that's what it'll
report to whoever asks --- clearly, this is wrong.

Similar misrepresentations may occur with XT machines and either the
autoconfiguration or dip switch settings.

This can be used in your favour if you wish to format the disk undersized for
whatever reason -- unfortunately, you can't format them oversized :-(.

If you use any of these methods (NU, infoplus, debug, etc), you're assuming
that the last person to muck around with the system configuration got it right
(either that or that the BIOS and the controller are actually smart enough
to snoop around the drive to work out how big it is).

It is wise to look at the label on the drive itself and from there to find out
from the spec sheet how big the drive actually is. Be careful to take into
account the type of controller (ie is it RLL?).

Earl
-- 
Earl Chew, Dept of Computer Science, Monash University, Australia 3168
EMAIL: cechew@bruce.cs.monash.edu.au PHONE: 03 5655447 FAX: 03 5655146
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