From: terry@cs.weber.edu (A Wizard of Earth C)
Subject: Re: Installing 386bsd
Organization: Weber State University  (Ogden, UT)
Date: Wed, 7 Oct 92 00:31:21 GMT

In article <1992Oct6.162100.12545@rhrk.uni-kl.de> andrick@sun.rhrk.uni-kl.de (Ulf Andrick [Biologie]) writes:
>terry@cs.weber.edu (A Wizard of Earth C) writes:
>: The DOS partition should follow the 386BSD partition on the disk; the
>: 386BSD partition has to be first.
>: 
>: The use of a 33Meg primary DOS partition is good; it means that the
>: "shutdown -todos" will work for you.
>: 
>: You didn't say if you are using IDE; if you were, select drive type 45
>
>German `AT-Bus' translates to IDE in English.
>
>: in the CMOS setup and enter in the actual number of heads/cylinders/etc.;
>: this may mean that you can't use all your drive, since DOS is dumb about
>: greater than 1024 cylinders.
>: 
>: Alternately, you can use the whole disk for 386bsd, in install sufficiently
>: to rebuild asboot and disklabel, and move the 386BSD partition to later
>: on the disk.  This will take a lot of work; installing 386BSD *and* DOS
>: on the same IDE drive is difficult.
>
>Is it? My partition tables make me believe that my DOS
>partition is the first on my disc and that 386BSD partitions are
>located after it. The DOS partition just happened to be where
>it is when I set up 386BSD by `install'. Do I face any major
>problems because of that?

This will have to change unless you modify the code which acts on the disk,
and assumes 386BSD is first.  Again, this is asboot and disklabel.

If you modify the drive type to set the correct geometry in the CMOS, you
will have to reinstall DOS.  You might as well put the DOS partition after
the 386BSD partition if you do this, since it will necessitate a reinstall
anyway. This may put all or part of the DOS partion(s) on or after cylinder
1024.  If this happens, you will have to use the alternate method, the
rationale of which is described below:

The only time 386BSD will work on a translated drive is if it gets the
whole disk or if the first sector of the 386BSD boot is in the same
location on both translated and untranslated sectors.  Some "modern" IDE
drives will actually remap locations non-linerarly on the drive (ie: 0 != 0
regardless of translation).  These won't work without the CMOS modification,
since the boot code will look in an untranslated location derived from
a translated address for that location.

Another possibility for DOS and 386BSD on the same drive with translation on
is if (1) the translation is direct linear (ie: the cylinder times the
number of sectors per cylinder plus the sector offset is the same location
the translation would get for the translated address... in other words,
sector 197 is the same in both geometries.) and (2) the location of the
DOS partition following the 386BSD partition on the disk is on a translated
sector boundry in excess of the last sector of the untranslated 386BSD
portion of the disk.  If this boundry happend to coincide with a physical
cylinder boundry, then the DOS partion may be usable by mtools.  The only
significant advantage to this is that DOS hates cylinders past 1024, so
you can still put DOS at the end of a *big* disk past physical cyliner 1024
but before translated cylinder 1024.

Either way, you will have to back up your DOS partition, since it can't be
the first thing on the disk, unless you choose to modify asboot, disklabel,
and family and pick a place where the physical and translated cylinder
boundries coincide for your 386BSD to live.

Note that turning off translation in the CMOS by picking appropriate settings
is dangerous even if the DOS partition is going to be first, since  you may
still have the DOS partition past the  1024, which would cause it to fail.


					Terry Lambert
					terry@icarus.weber.edu
					terry_lambert@novell.com
---
Any opinions in this posting are my own and not those of my present
or previous employers.
-- 
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