Ah! SDHC.

So, SDHC cards are a little different than regular SD cards (the protocol used to communicate with the card is a little different) and often aren't supported by particular SD card readers like potentially the SD-to-IDE adapter you're using.

(I know back in the day, I hacked my Nintendo Wii, which involved loading a bunch of homebrew programs on an SD card, and at first it didn't support SDHC cards until there was a firmware update.)

Technically, I think any SD card can be SDHC, but almost always SDHC is only used by high-capacity cards. Also, I think they usually say "SDHC" physically on the card.

So, probably the next thing I'd try if I was you was to change out your SDHC card for a non-HC SD card. Any 8GB to 32GB card should be fine, I'd think. (If you have any that are smaller even than that, like 256MB, even, you could at least use it to confirm that's the issue. You just couldn't expand the partition sizes out to 2GB.)

There has to be a way of getting FreeDOS onto the SD card. Way back when, there used to be ways of getting a floppy disk (and hard drive, I did it a few times) bootable with the SYS command to write the boot files to the right places. That was MS-DOS, though.

Hmm.

This article seems like it could be helpful.. It's for creating a disk image, not a drive, but the commands should work if you substitute in the SD card you want to use.

Please note that I haven't actually tried any of this. I'm at work and trying to pull together what scraps of knowledge I still have from my DOS days into something that seems coherent. This might not work, so please treat it as kicking some ideas around over coffee right now!

ms-sys basically does the same thing that format /s and sys a: used to do back in the days of DOS. That makes a drive bootable. So, you'd partition and format your SD card as VFAT or FAT32 from your box (I don't know if you have a Linux box or a Windows machine, or what). I'm guessing it'd be something like this:

sudo fdisk /dev/mmcblk0

# New DOS disk label
o

# New partition.
n
p
1


t
c
a
1
w

Format the partition on the SD card:

sudo mkfs.vfat -c -v -F32 /dev/mmcblk0p1

Then use ms-sys to write the MBR to the SD card.

sudo ms-sys --mbrdos /dev/mmcblk0p1

Mount the SD card. Download FreeDOS and uncompress it. I think that would be FD13-FullUSB.zip. There doesn't seem to be a downloadable archive of "Here's all the stuff that's in the disk image," just the disk image. Some gymnastics do seem to be required to mount it:

sudo losetup /dev/loop0 FD13FULL.img
sudo fdisk -l /dev/loop0

Disk /dev/loop0: 512 MiB, 536870912 bytes, 1048576 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000

Device       Boot Start     End Sectors   Size Id Type
/dev/loop0p1 *       63 1048319 1048257 511.8M  e W95 FAT16 (LBA)

The gymnastics in question have to do with mounting a partition of the disk image, because you can't just set up the disk image and manipulate it like a disk device. In this case, it's calculating where to mount the FreeDOS partition: sector size * first sector == 512 * 63 == 32256

sudo losetup -d /dev/loop0
sudo losetup -o 32256 /dev/loop0 FD13FULL.img
sudo mount /dev/loop0 /mnt

From there, it looks like you'll have to look at /mnt/setup.bat to figure out how to do a manual setup of FreeDOS on the SD card. There is also a /mnt/FDOS-x86/SETUP.BAT file that I think will have to be read through to get the process figured out.

Again, this is all theoretical. I've no idea if it'll work without tinkering with it on real hardware. It's as close to figuring out how to do a manual installation as I have time for right now.