Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!waikato.ac.nz!canterbury!phys169
Newsgroups: comp.sys.ibm.pc.misc
Subject: Re: HELP I'M BEING HELD CAPTIVE BY AN XT
Message-ID: <1991Jun5.105556.949@csc.canterbury.ac.nz>
From: phys169@csc.canterbury.ac.nz
Date: 5 Jun 91 10:55:56 +1200
References: <10177.283d9e6a@ohstpy.mps.ohio-state.edu>
Organization: University of Canterbury, Christchurch, New Zealand
Lines: 43

In article <10177.283d9e6a@ohstpy.mps.ohio-state.edu>, smithj@ohstpy.mps.ohio-state.edu writes:
> A friend of mine is forced to use an original IBM PC-XT with a 10Mb HD.
I bet it doesn't have a partition table. That's the first source of confusion.

> When he received it we erased everything and reformated the drive using the
> FORMAT command under IBM-DOS 2.10.  Everthing worked fine.  He then bought
> IBM-DOS 3.30 and installed that system (including command.com in the root).
> But when we rebooted the computer it just hung. 
That's happened to me. The problem basically is:

DOS stores information in the boot sector, such as how many sectors each FAT
takes. For some stupid reason, DOS often ignores that information, and goes by
its own estimation of where things should begin. Unfortunately, this varies
between versions of the operating system, and the calculations used by the boot
program when you start up are different to the calculations used while the
thing is running. So you can boot from a floppy and see all the files on a hard
disk okay, then try booting from it, and everything is wrong. The only DOS to
pretty consistently get it right seems to be DRDOS 5. The factors that make the
most difference are: 
(1) the difference between DOS 2.x and DOS 3.x
(2) smallish drives, where some O/S's choose 12-bit FATS and others 16-bits
(3) not having a partition table. Mainly a problem for those trying to install
    new software "by the book" and wondering why it doesn't work.
(4) The fact that some drives formatted under different versions of operating
    system can be accessed when you boot from floppy, but not from the drive
    itself.

As an interesting exercise, you might like to boot from DOS2 and DOS3 (and even
DRDOS5) floppies, and run Norton's NU on the drive, seeing where the root
directory seems to be.

The solution is to either install DRDOS 5 (which seems to work with anything),
or boot from whatever version of DOS will read the disk, copy everything off 
that you need, reformat the disk (a good opportunity to use HDDIAG or some
other good disk utility to look for bad blocks and low-level format), then
boot from a floppy containing the version of O/S you want, and FDISK then
FORMAT then SYS the disk. Note that a low-level format *shouldn't* be needed,
but is a good idea, partly because I have once or twice come across a hard disk
with a bad block in an area important to the operating system when it was
loading, which made me think there was a software fault.

Hope this helps,
Mark Aitchison, Physics, University of Canterbury, New Zealand.