formathd

                        Hard Disk as Superfloppy Tools

Tools for preparing a hard disk with a superfloppy format for use with DOS
operating systems.

Requirements:
 * 8086 PC with 192kb RAM (128kb free)
 * MS-DOS 3.31 or newer
 * Hard Disk with 512 bytes per sector
 * BIOS service int 13h ah=08h that works (no EZDrive)

It was published at https://retrocomputing.stackexchange.com/a/20309/418 that
it has long been known that DOS or Windows 9x can be patched to be able to
access a hard disk formatted with a single giant FAT filesystem.

This is convenient because it is then possible to mount the filesystem from
the host operating system and copy files in and out without messing with offset
or any other such nonsense. This also saves 31KB of disk space.

This project sets up the filesystem from inside operating system rather
than from any host operating system (and thus should work on bare hardware).

Installation instructions for a VM guest:

ALL DATA ON THE TARGET DISK WILL BE ERASED.

1: Prepare a MS-DOS boot floppy for the version of DOS you want to install.
   You will need FORMAT.COM and SYS.COM and whatever to access install media.
2: Copy PATCHDOS.COM and FORMATHD.COM to it.
3: Boot the floppy.
4: Run PATCHDOS.COM A:\IO.SYS
5: Run FORMATHD.COM 0 /16
6: Boot the floppy again
7: Run FORMATHD.COM 0 C:
8: Boot the hard disk
9: Install DOS
10: If DOS doesn't boot after install,
    Boot the floppy again
11: Try DIR C: to see if you can read the disk.
    If you can't read the disk,
12: Run FORMATHD.COM 0 /F to repair damage done by OS install and reboot
13: Run PATCHDOS.COM C:\IO.SYS

If preparing on a physical machine, you will need to know the BIOS disk ID
and what drive letter the hard disk will end up on. It would be wise to
disconnect any other hard disks so you end up with 0 and C: to avoid risk
of data loss.

I have verified these instructions on MS-DOS 6.20 and Windows 95 under QEMU.

Copyright (C) Joshua Hudson 2021, 2023 Licensed under CC-BY-SA 4.0