12 Apr
2004
12 Apr
'04
8:18 p.m.
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