Making foreign DOS boot floppies (IBM).

From: Fred N. van Kempen <waltje_at_pdp11.nl>
Date: Tue Apr 13 03:18:13 2004

On Mon, 12 Apr 2004, John Allain wrote:

> Nice. Looking up SYS.COM in the Ref (v3.3) manual:
> "DOS statrup requires {(sic)IBMBIO.COM and IBMDOS.COM}
> to occupy the first two directory entries, and because
> IBMBIO.COM must start at the beginning of the data area of
> the disk." that explains a lot.

The older boot sectors loaded IO.SYS (IBMBIO.COM for PC-DOS) as
first entry, using the cluster mapping found for the first entry
in the root directory, and then the same for MSDOS.SYS (IBMDOS.COM
for PC-DOS) using the second entry in that root directory. I do
remember there was some level of magic checking- but afaik, they
took that out fairly quickly.

So, assuming a blank diskette:

1. Format it with FAT(-12)
2. Make *sure* the first two directory entries are blank, which
    includes no volume label being present (== dir entry !)
3. Copy those two files over.
4. Patch the boot sector.
5. Copy COMMAND.COM and any other files.

This has always worked for me. But, yeah, as someone already
pointed out, it is much easier to just archive bootable images
of these diskettes :)

--f
Received on Tue Apr 13 2004 - 03:18:13 BST