MS-DOS 1.x

System

MS-DOS 1.x

Originally 86-DOS, written by Tim Paterson of Seattle Computer Products, DOS was a rough clone of CP/M for 8086 based hardware. Microsoft purchased it and licensed it to IBM for use with Microsoft's IBM PC language products. In 1982, Microsoft began licensing DOS to other OEMs that ported it to their custom x86 hardware and IBM PC clones.

Read the full story here

Mousy54

WINIMAGE

In order to make 160kb and 320kb DOS disks readable in WINIMAGE,
the following changes should be make to the floppy disk header.
This is the first 30 bytes of the disk. You will need a hex editor for this.
These modifications should work for most disks in WINIMAGE, and most disks
should boot in DOS. There is one known exception, although it is readable
in WINIMAGE, COMPAQ will not boot up if this change is made. Also this
will not work for the infamous boot disks, since there are no files to see.
As always NEVER attempt this on the original disks, make a copy.

5¼" disk
ADDRESS | BYTES | 160 | 320 |
------- | ----- | ----- | ----- |
00-02 | 00-02 | DO NO CHANGE | jump code
03-0A | 03-10 | OPTIONAL INFO | optional OEM name and version
0B 0C | 11-12 | 00 02 | 00 02 | bytes per sector
0D | 13 | 01 | 02 | sectors per allocation unit
0E 0F | 14-15 | 01 00 | 01 00 | reserved sectors
------- | ----- | ----- | ----- |
10 | 16 | 02 | 02 | number of FATs
11 12 | 17-18 | 40 00 | 70 00 | maximum number of root directory entries
13 14 | 19-20 | 40 01 | 80 02 | number of sectors in logical image
15 | 21 | FE | FF | media descriptor byte
16 17 | 22-23 | 01 00 | 01 00 | number of sectors occupied by a single FAT
18 19 | 24-25 | 08 00 | 08 00 | sectors per track
1A 1B | 26-27 | 01 00 | 02 00 | number of heads
1C 1D | 28-29 | 00 00 | 00 00 | # of hidden sectors

vio08

@Mousy54 Thanks! I'll use it when I need it.

DeFacto

In other words, you just add an appropriate BIOS parameter block (BPB) to its standard location from DOS 2.0 and later.

Mousy54

AH, I don't know, could be.
Although it is probable they are out there, I don't recall ever seeing a 160kb disk in DOS 2.x and above and as I remember all the 320kb disks I looked at cannot be naturally seen by WINIMAGE. I have also seen 180kb and 360kb that cannot be seen by WINIMAGE.
What I did is read up about all the specs for all DOS disks from 160kb to 2.88mb.
Once I understood how the disks where laid out, I created a small table listing all the parameters. After that I thought why not try it out on the invisible disks and it worked. Since I have not seen it anywhere on the internet, I thought I would share the information for others to use if they wish to.

DeFacto

The disks themselves aren't really "invisible", WinImage just relies on the BPB exclusively to figure out all the parameters. Without the BPB, you'd have to check the media descriptor byte in the FAT, image size, etc. to be sure what kind of disk it is, which WinImage doesn't bother doing.

Mousy54

I know that they are not invisible, just called them that, bad chose in words I guess. Yes, that is what I kind of figured out after all my reading.

Mousy54

BTW: MS-DOS 1.25 [Zenith Z-100 PC] (5.25-320kb) contains 360kb images, not 320-kb images.

SomeGuy

Thanks for pointing that out. I've updated the download. It is actually supposed to be 320k, but that was a crufty copy. Oddly this adaptation of 1.25 actually supports 360k.

This 1.25 floppy disk was actually bundled with Zenith's MS-DOS 2.11, I presume to increase software backwards compatibility for their machine. So it is also in the 2.11 download, but I've separated out a copy to make it easier to find.

The file contents of the crufty copy were otherwise identical.

Mousy54

I thought it should be a 320k. I adjusted my copy to 320k before I commented and mostly it matches your new copy.

Legacy OS

I have created Tutorials on how to install DOS 1.25 on 86Box and PCem.
https://tutorialsonlegacyos.blogspot.com/2021/05/how-to-install-dos-125-in-86box.html
https://tutorialsonlegacyos.blogspot.com/2021/05/how-to-install-dos-125-on-pcem.html

Mousy54

For MS-DOS 1.25 [Compaq OEM r1.10 Rev B] (5.25-320k):
the MS-DOS 1.25 [Compaq OEM r1.10 Rev B].txt file states "This archive contains one 320k disk image in raw and ImageDisk disk format.
The imageDisk is missing.

SomeGuy

Thanks for pointing that out. I usually include an ImageDisk image with any disk that can not open in WinImage (which includes most DOS 1.x disks).

I'll get that re-uploaded but in the mean time, you can convert a 320k IMG file to Imagedisk using the command:
BIN2IMD DM=5 N=40 SS=512 SM=1-8 /2

Mousy54

Thanks
Yes I noticed that almost all of them include an ImageDisk file.
I'll give BIN2IMD a go.

CreepQ

"The command interpertor supported the following commands" needs to be "The command interpreter supported the following commands"

SomeGuy

Ok, corrected. Thanks for pointing that out.

SimpleDiskette

I Believe there was never an MS-DOS 1.00 because at the time when Microsoft made their own fork of PC-DOS, PC-DOS was already on 1.25 at the time and nobody would want a downgraded older version so they figured it was worthless to make a version for 1.00. If you want a true "1.00" of this DOS, you're gonna want not MS-DOS but PC-DOS, there they have 1.00 and a pre-release as well.

md_yx

downloaded the "MS-DOS 1.25 [Eagle PC OEM]" loaded it into an emulator as a .img file (the emulator had 64 kbs of ram, and an emulated 8086), it just displayed some random characters, random symbols, before crashing:
*Undefined opcode 0xFF at 0x00007C00
stopped (21625937 cycles, 11907 ms, 1816237 hz)
AX=0000 BX=7C00 CX=0004 DX=0000 SP=0100 BP=E4B7 SI=0002 DI=0044
SS=0030 DS=0040 ES=0000 PS=F296 V0 D0 I1 T0 S1 Z0 A1 P1 C0
&0000:7C00 FFFF INVALID
Then i tried the MS-DOS 1.25 [CDP OEM], and that one worked for some reason. No idea why the first one didnt work.

SomeGuy

What emulator was that?

The Eagle PC OEM will run on some emulators.

Please keep in mind that many of these OEM releases were only intended to run on the vendor's specific hardware. Even if an OEM release runs on a genuine IBM PC, it may have problems running on other clones or emulators.

OEM versions may poke around for hardware that an genuine IBM PC does not have, make buggy use of BIOS calls that only happen to work on an IBM PC, or hard code assumptions - for example a genuine Eagle PC/1600/PC Spirit will always have a minimum of 128k.

One of the interesting things about the Eagle PC OEM is that it supports a "Quad Density" (96TPI) 800k format used by the Eagle 1600 which came with 96TPI drives. This format is somewhat unique in that it uses 1024 byte sectors rather than the standard 512. I forget how well 1.25 works, but on Eagle's DOS 2.1, you can boot on an IBM AT compatible computer and use a 1.2mb drive to access these oddball formatted disks.