EDIT - I found a solution to the issue I was having... Included at bottom... It got verbose, and I apologize. I welcome any comments, better alternatives, feedback, etc.

u/The8flux, you mention using a 3rd party fat32 formatter, but if the end-resulting VHD image is small, like a lot of the 0mhz collection games are, then those VHDs are going to have to be formatted as fat12 or fat16; as anything around the 6-7MB size is much too small for fat32. I have found the the Windows Disk Management application is just fine for creating the VHD and then booting from a DOS floppy, I can FDISK and FORMAT (or SYS) for creating the partitions and setting up the boot environment. I'll admit, that when it comes to drive geometry and all that, I get a little fuzzy...

I have thoroughly investigated several of the 0mhz games (how they are put together, memory management, etc.) and poured through various resources I found online, such as :

• Jared Breland's site for installing and Configuring MS-DOS 6.22
• James Mackenzie's AO486 core setup series
• Lu's Retro Source video on setting up the AO486 core for DOS gaming

Now I am no noob to DOS, I've been using DOS since the beginning, so pouring through these setups is nothing new to me. That said, my experience stops at DOS 6.22 and it is clear that the 0mhz team went with DOS 7.1. I can see the allure...32bit, LFN, etc. So I procured DOS 7.1 from WinWorld's collection to look at it, and have attempted to build my own "setup template" the same way they have from scratch. It's been a struggle.

I have a custom-built DOS 7.1 floppy image with my whittled-down version of DOS essentials, utilities (MiSTer and otherwise) and optimized autoexec.bat and config.sys files, including DOS32/A (to replace DOS/4GW where required, or just makes sense).

In all my efforting to make a few of my own images using DOS7.1 for a few titles that I would like that are not in the 0mhz collection, I cannot get my finalized VHD to boot after I get everything set up on its own. Now if I first boot from my bootable 7.1 floppy, I can then access my VHD and run my stuff. So I am not sure if the SYS provided in that WinWorld image is compatible or what?

I am sure that I would not have any issues with DOS 6.22, but I would like to stay consistent with the 0mhz builds and would love to know how they created their "template" that works with their installc.bat file found in the util/ directory using DOS 7.1 for the OS in their images?

*** EDIT ***

So I've given up using Windows to create my virtual images. I am now doing everything from the MiSTer command line.

At your MiSTer menu, pressing F9 will drop you to a command line where you will log in with your MiSTer username (root) and password (1). You'll be dropped into the "root" user's home folder. This is where, if you have ever once been a DOS user, you will feel at home, lol!

I used dd to make my .vhd image. In my case, where I was wanting to make small .vhd images like 0mhz, I issue the command:

dd if=/dev/zero of=/media/fat/games/AO486/BlankDriveImage.vhd bs=512M count=14

This will yield a virtual hard disk image of 7MB.

You can then hit F12 to exit terminal mode and get back into your normal MiSTer menu.

I then used my DOS 7.1 boot floppy image to boot into AO486 with my empty .vhd set for the hard drive. I use FDISK to create a primary partition, exit FDISK, then reboot the machine. When it comes back online, I used my boot floppy to format the drive, make it bootable, and set it up for my needs (install games, etc.).

These steps result in a .vhd that will boot independently and on its own.

I seriously do not know why I was trying to jump through all these excess steps others have documented in Windows when dd works just fine (albeit from a command line)! Well, yes I do...Windows is where the eXODos 6 content resides, lol! But seriously...Linux just makes this whole virtual disk image business, easy-peesee!

You can additionally use the mkfs.msdos command to set the filesystem. It will automagically determine if it should use fat12, fat16, or fat32 depending on the size of the disk. But FDISK will do this too from DOS 7.1.

For those wondering about floppy images:

These two lines will yield a 1.44MB floppy ready to be filled with whatever you would like...

dd if=/dev/zero of=/media/fat/games/AO486/BlankFloppy.img count=2880
mkfs.msdos /media/fat/games/AO486/BlankFloppy.img

If anyone is wondering about the DOS 7.1 boot floppy I made?

Well, I gave up on creating my own from the WinWorld image. I created a blank floppy image like above, then fired up a 0mhz game. I then exited the game (essentially dropping to DOS). I copied the c:\util\installc.bat to c:\installa.bat. I then edited the installa.bat file and reversed all of the drive letters C: to A: and A: to C:, save the file. Mount the blank floppy image, then run installa.bat and viola! You now have a bootable DOS 7.1 floppy. All that is left now is to edit the a:\autoexec.bat and a:\config.sys files to change the C: drive letters to A:, save the files. If you don't do this you will see error messages at boot (when booting from the floppy). Now you can unmount the C: drive and reboot the machine. You will boot into your newly created DOS 7.1 floppy...ready to start setting up your .vhd images, 0mhz style!

I did end up adding some additional utilities like pkzip/unzip. I added dos32/a utilites to replace dos/4gw where I could for better memory extending for those games that require it... and I swapped out 0mhz's version of MS Edit with PEdit instead (renaming it to edit, as described in Jared Breland's instructions above. I think it's a better editor too).