This sounds like the sort of problem you get when you haven't rebooted properly. But you say FDISK did the reboot, strange. Try FDISK /mbr from dos 6.22. Is it possible to write the partition table in a different machine with a normal IDE setup?

lorecast162 wrote on 2021-10-06, 21:11:

I have DOS 3.3 on a floppy (some NEC OEM version I used, dont ask me why, it was my only choice) and launched FDISK to create the partition.

File systems were in flux at that time - there is FAT12, initial FAT16, and the modern variant "FAT16B" used today.
https://en.wikipedia.org/wiki/File_Allocation_Table#FAT12
It could also be something with the partition type field in the partition table.
You have no way to make a DOS 5 boot floppy and try there? Who knows how "some NEC OEM version" may work, in those times I think MS distributed DOS in source form and the OEM was expected to customize IO.SYS, and who knows what they did...

jakethompson1 wrote on 2021-10-07, 02:39:

You have no way to make a DOS 5 boot floppy and try there? Who knows how "some NEC OEM version" may work, in those times I think MS distributed DOS in source form and the OEM was expected to customize IO.SYS, and who knows what they did...

Hmm... I can try making one using https://winworldpc.com/download/28c2b366-26e2 … ad-11c3a5c28f13, it seems to be pretty damn close to the original.
For some reason back when I first got this computer I was hell-bent on using 3.3, can't even remember why.
Can I use this on my 486 and the CF with an IDE adapter and install DOS on it? I highly doubt a XT clone with 512KB will unzip a >1MB ZIP file to memory...

mR_Slug wrote on 2021-10-07, 00:22:

This sounds like the sort of problem you get when you haven't rebooted properly. But you say FDISK did the reboot, strange. Try FDISK /mbr from dos 6.22. Is it possible to write the partition table in a different machine with a normal IDE setup?

I can try, but I don't have a CF->IDE adapter so I'll have to wait at least until next week.

The FAT issue shouldn't be an issue if the bootable DOS floppy has the same version of fdisk and format on it. Mix and match will lead to problems as stated above. I've not used CF cards much, but have heard they have incompatibilities sometimes. The usual advice is to try another card.

Alright.
I managed to make a DOS 5.0 disk that boots on this computer, copied FDISK, FORMAT and SYS to it.
I think the 32MB card is busted as doing anything just throws errors.
I tried with a 128MB Cisco CF card and the partition on it is visible (installed DOS 5 on it through PCem with a dd'ed image and wrote it back to the card) and readable from DOS 5.
Running FDISK /MBR prints no messages on the monitor but running fdisk by itself says "No fixed disks." or something like that.
I cant boot from it either as it just says "Non-system disk or disk error. Replace and press any key when ready", probably because I succesfully nulled out the MBR...
I guess I have to get one of those industrial cards from Transcend with Fixed Disk mode (I have a retail 256MB but its set to removable disk mode apparently)...

lorecast162 wrote on 2021-10-10, 20:17:

I cant boot from it either as it just says "Non-system disk or disk error. Replace and press any key when ready", probably because I succesfully nulled out the MBR...

that message comes from the PBR Partition Boot Record, not the MBR.
you might want to try a format or a sys.

weedeewee wrote on 2021-10-10, 20:33:

lorecast162 wrote on 2021-10-10, 20:17:

I cant boot from it either as it just says "Non-system disk or disk error. Replace and press any key when ready", probably because I succesfully nulled out the MBR...

that message comes from the PBR Partition Boot Record, not the MBR.
you might want to try a format or a sys.

After doing SYS C: I get the same error.
Same thing with FORMAT C: /S