I'm moderately sure that the 98 boot sector can load any old version of dos.

The way to enable it is pretty simple.
You rename msdos.sys, io.sys, command.com,autoexec.bat and config.sys to *.dos

And you enable the oldmsdos menu in the 9x msdos.sys

You don't need any special tricks. Just copy those files to root.

Now, it might be possible that it will simply load whatever of those files are correctly named.

Ie, the 98 boot sector and dos 5.0 io, msdos, command, etc.

In which case, it wouldn't be that hard to write a config.sys menu and autoexec bat that renames any and every version you want and reboots.

Eg
Copy msdos.50 msdos.sys
Copy io.50 io.sys
Copy command.50 command.com

Etc
Reboot

The trick will be putting the menu autoexec and config sys back at the end of every version's autoexec - probably best to call another bat on the last line so it doesn't error.

If it won't simply load that way, you'll have to figure out the same thing but renaming them as *.dos and probably whatever flag is set when/if windows reboots to old msdos.

Might help
https://www.mdgx.com/msdos.htm

Especially BootMulti= and BootWin=

Found this too
booting multiple dos version on one machine.

I'd suggest using memdisk with either grub or isolinux, and booting small hard disk images from the CDROM, rather than floppy images.

you can have as many on there as will reliably fit, and with a DVD image, that's... A LOT of possible images.

Grub4dos is capable of chainloading IO.SYS (or the appropriate equivalent like kernel.sys) of most DOS versions. So you can have a single partition and a menu.lst for Grub that presents the user with a menu to choose an IO.SYS to boot from.
If Grub4dos is not able to boot some particular flavor of DOS, you can still use it - either by chainloading a saved boot sector or by booting a disk image. Unlike memdisk, Grub can do nested images and images larger than available RAM.

Again, just straight up isolinux/grub2, and memdisk.

memdisk gets loaded like a linux kernel on the menu item in the list, with the disk image it will serve as the initrd. It hooks int15, and int13, to subtract the appropriate amount of memory from the extended memory pool, then uses less than 1k of conventional memory to provide INT13 services to the disk image.

feed it some very small 5mb or so disk images. This leaves the diskette drives free for actual use, and does not need the CD in the drive after booting (since the whole image gets copied to RAM.)

You can even boot windows this way.

I recall using a tool called "MagicISO" to do exactly this.

It allowed you to create CDs/DVDs which have different boot images and you would
select which one via an on-screen menu when it booted.

I used it to make a DVD with stand-alone bootable systems for various
test environments, some of which used different OSs.

Dave ::: https://dunfield.themindfactory.com ::: "Daves Old Computers"->Personal

Thank you all for your replies so far.

@myne
I was under the impression this option was only for having Windows + 1 DOS version, and I've also read somewhere that it had some issues; it's one of my least favorite options, but I will give it a try and see how it works.
And thank you for the link to the other thread 😀

@wierd_w and kmeaw
I've used Grub4dos as well as isolinux and memdisk in the past for other projects, and I feel they may be the best approach. Thanks for the details on each, especially the idea of using small hard disk images; for some reason I had forgotten this was a thing.

@DaveDDS
MagicISO would fall under scenario #2 (Boot CD (emulated floppies)).
I will check MagicISO to see if it offers additional features that may be useful.

Keep 'em coming 😀

Memdisk-hosted DOS instances still probe for other DOS-readable partitions on the actual disk controller(s).

Because of this, if used in a retro machine, I'd suggest a 'communal' ext-dos partition + logical drive, that is readable by all DOS versions you intend to have available. (This means 32mb tops, if you are using Dos 3.x) This way the boot drive only contains the OS, and is hosted by memdisk, but the communal drive is always accessible, writes are permanent, and can be where any menu system or dos games live.

Using say, a linux ext2 volume as the actual bootable partition (with GRUB), with all the disk images hosted there, would net you all the different envirionments you could ask for, including 'very hard to break' copies of win9x, if you have sufficient ram to devote. (Need 256mb to do realistic win95A+ plus!pack, 384mb for win98 oem, and 512mb for win98SE, assuming you turn on drivespace 3, and ultrapack the bejeebus out of them. I've delved into this quite aggressively in the past.)

wierd_w wrote on 2024-09-17, 14:23:

all the different envirionments you could ask for, including 'very hard to break' copies of win9x, if you have sufficient ram to devote. (Need 256mb to do realistic win95A+ plus!pack, 384mb for win98 oem, and 512mb for win98SE, assuming you turn on drivespace 3, and ultrapack the bejeebus out of them. I've delved into this quite aggressively in the past.)

It brings me back memories of an internet cafe I used to visit in the past. They used compressed ramdisks to boot win98 to reach two goals - provide the user with a very limited free "disk" space (extra was available for premium on request) and have a fresh system on each boot (so if a user breaks something, a reboot will fix it).

pool7 wrote on 2024-09-17, 12:47:

Keep 'em coming 😀

Couple other thoughts....

I didn't even think if these since I'm so used to them - all my systems have removable hard drive
"carriers" - you can easily pop out one drive and put in another (with system powered off obviously).

Another good option if you don't need a "real" machine.... Check out my DBBD tool (DosBox BootDos)
It automates booting from various DOSes ... I happen to use a good sized RamDisk, so for me it builds
a DosBox that autoboots the selected DOS there.

I have MS-DOS, PC-DOS, FreeDos, CalderaOpenDOS and PTS-DOS set up
for it. (I'll add DR-DOS if I find it again)

These boot under DosBox which has VERY good hardware emulation (needs to be
for games) but since it boots the actual OS, DosBoxs "quirks" are not really seen.

My DOSs boot from virtual-floppy and set up a good sized RamDisk as C: .. I've got a more
permanent setup on a virtual hard drive which actually boots C:

Dave ::: https://dunfield.themindfactory.com ::: "Daves Old Computers"->Personal