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MS-DOS 2 on single-sided floppy?

seat safety switch

seat safety switch

Experienced Member
Joined
May 24, 2018
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Alberta
Hi all,

I've got an MBC-555 (original recipe: two single-sided Teac FD-54As) and I'd like to run MS-DOS 2. What finally pushed me over the edge is that Kermit needs it, and I'd like to use Kermit to test my homemade serial card:

sanyo-mbc555-kermit-needs-dos-2.png

Problem is, the only MSDOS 2.x image I've been able to find is for double-sided floppies. Is there a way to easily convert an image to single-sided, or are there single-sided ones floating around?

Another option I've considered is configuring MAME to use a double-sided drive in A:, and then boot off of it and format a blank floppy in B: with DOS system files. I'll probably try this first... but I'm not sure if that would require tweaking of IO.SYS, or if it's even possible to have a mixed-format system with the way that drive configuration works.

Thanks in advance for any help.
 
Winimage makes it easy to resize the image for a single sided format with the Change Size option in the Image menu. Note that the disk has to have less than 180K of files so fully loaded DOS boot disk images won't be resized.

If you can boot any system with DOS 2, making a single sided bootable disk is straightforward. FORMAT /1 /S would be the command IIRC. No changes to any system file; the disk just doesn't have much free space.

The PCJS emulated XT is launched from 180K (single sided) DOS 2.0 disk images. That may be something to try out. https://www.pcjs.org/machines/pcx86/ibm/5160/cga/ Select save to get a copy of the image.
 
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Thanks! I don't think I can use IBM PC/XT disk images because the Sanyo, being a weird little thing, loads part of its DOS BIOS into RAM from the boot sector and IO.SYS, but I will try resizing the image using WinImage. I tried doing it by hand but I suspect I ended up mangling the FAT pointers.
 
I would have expected that as well, just to retain compatibility with the original IBM PC.

I looked at the images at winworldpc and they seem to be 180K, so that matches up.

I’ve got an early driver disk for AST cards and it’s also single sided, probably for the same reason.
 
I've also confirmed that with the fading pink-labeled floppies for PC-DOS 2.
Of course, in light of the thread title, this once again provokes the question "Is PC DOS the same as MS DOS?" :)
 
krebizfan said:
If you can boot any system with DOS 2, making a single sided bootable disk is straightforward. FORMAT /1 /S would be the command IIRC. No changes to any system file; the disk just doesn't have much free space.
Click to expand...
This seems to have been the demon tweak that worked out for me, thank you! I took a 180k single-sided image and booted MAME as follows:

Code: 
% ./mame mbc55x -flop1 roms/mbc55x/Sanyo_DOS_v2.11.img -flop2 empty.dsk

Then, after checking that the emulator believed that the disk on B was indeed 180k, I did FORMAT /1 /S B: and consented to everything it wanted.

Screenshot 2023-12-28 at 8.00.35 PM.png

The result seems to be a 180k disk image that's bootable in MAME with COMMAND.COM loaded on it, but I haven't tried it on the real machine yet. I seem to recall I tried this before, but without the /1 option, and ran into trouble (there's no /? switch on the FORMAT for this version so I wasn't aware of what switches it supported.)

Thanks to everyone for your help, I will update when I test to see if this is viable. PC-DOS sadly doesn't work on the MBC-55x because of its weird BIOS, at least according to the readme shipped with the copy of DOS 2.11 for MBC-550 I found on WinWorldPC:

Microsoft MS-DOS 2.11 [Sanyo MBC-550 OEM r1.00]
Released in 1984 by Sanyo/Microsoft
For Sanyo MBC-55x computers ONLY

This is the custom version of MS-DOS required to operate a Sanyo MBC
55x computer. The Sanyo 550 is not fully IBM hardware compatible, and
will not run PC-DOS or generic MS-DOS.

This software will not boot on an IBM PC or 100% compatible, only on
the Sanyo MBC.

This archive contains one 360K disk image in ImageDisk and Raw
format.
Click to expand...

One immediately interesting thing is that the DOS 1.2 images I have are all 8-sectors-per-track images, and the DOS 2.11 disk I just made has nine sectors. As well, the FAT seems to expand to two sectors each for primary and backup FATs.

I have a suspicion that this is not entirely true for MS-DOS 2.x but that will take a visit to the hex editor to poke through this first.
 
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seat safety switch said:
I have a suspicion that this is not entirely true for MS-DOS 2.x but that will take a visit to the hex editor to poke through this first.
Click to expand...

My recollection is that basically all the INT13 BIOS hooks that are in ROM on an IBM PC clone are implemented in RAM-resident software on the MBC-550, so it’d take a substantial amount of work to patch a PC compatible MS-DOS to work on the Sanyo.

... or maybe just swapping out IO.SYS and hacking the boot sector? I dunno.

 
I have a sanyo with both a dual and a single drive i could probably write you a single sided copy, as i have made in the past just as a test, do you have any other software? i have some business software we have had since i was a kid, but am looking for more, maybe we could mail swap copies if you have some?
 
I've only got the Sanyo DOS 1.25 image that I wrote a few years ago, but I would like to get an assembler (that's a little better than DEBUG, at least) and Kermit on there to test out my serial card. I still have yet to test the image I formatted through MAME.
 
let me know if your image works, if not you can mail me a blank floppy and ill copy 2.11 dos on a single side for you
 
jeffdai said:
let me know if your image works, if not you can mail me a blank floppy and ill copy 2.11 dos on a single side for you
Click to expand...

Thanks – the modified image did not work, it boots in MAME but not on the real machine. The image truncated with WinImage's "Change Format" menu item to 180k didn't boot at all in MAME, so I didn't bother trying to write a disk from it.

I'll try the FORMAT /1 /S technique again on the real hardware with my Gotek (I also have a double-sided drive that should work out of an MBC-1100) and see if that produces anything different, but if not I'll be in touch with you to try and figure out how to send some disks! Thanks for the offer.
 
I had the same issues writing teledisk images, they would not boot on a real machine when written back, only on the emulator. I dont mind copying them at all if it doesnt work this time.
 
I temporarily stuck a double-sided-capable Gotek into it to load up the Sanyo MS-DOS 2.11 image from WinWorldPC, and that seems to have booted.

sanyo-mbc555-msdos-211-boots-gotek.jpg

Next step is to figure out what I broke on the keyboard, and then see if I can format a blank disk using this environment. Hopefully the keyboard fix is just something silly I did while I was socketing the 8049, and I don't have to make an adapter.
 
It turns out it was simple: when I desoldered the 8049 from the keyboard, I put in a socket and then forgot to actually solder up all the pins. The EA pin was floating as a result.

sanyo-mbc555-keyboard-missing-mcu-pin.jpg

You may also notice that I also pulled the pad for pin 1 when I was desoldering it, but thankfully it's not connected to anything... the keyboard's PCB is in really bad shape (layers coming apart on the other corner of the PCB) so I would like to pretend it wasn't entirely my fault.

Good news is: once the keyboard was working, I managed to boot off the double-sided image on my Gotek and then write out a single-sided floppy that I could reliably boot from. Then, I dumped that floppy using the Greaseweazle.

I haven't had a chance to figure out what's different between the floppy that I can boot from and the floppy that I wrote from the sector image, but I'll probably get around to it sometime. You can download my (very minimal; just COMMAND.COM and DEBUG.COM) single-sided MSDOS 2.11 image for the Sanyo MBC-550/MBC-555 here. It's in SuperCard Pro format, which is supposed to be pretty good for non-copy-protected preservation. You should be able to convert this to a sector image format for an emulator, if for whatever reason the existing double-sided MSDOS 2.x images are not sufficient.

Next step is to get LINE55.COM and Kermit on a disk and try it with the serial card. I think I'll probably just end up using the Gotek for this task as well. Hopefully I made the serial card properly... 🤔
 
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