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DOS not booting off CF card?

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First post, by Boohyaka

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Hi there!

I installed a CF-IDE adapter and also tried a PATA-SATA adapter with a 2.5" SSD in my 486. Both are working fine, BIOS HDD auto-detects everything fine, for the SSD LBA is supported so I can get up to 8GB out of it. The computer is happy to work with these devices, fdisk them, format them, copying stuff, running games and installing DOS, everything works perfectly but one thing: DOS won't boot directly off of them. In both cases (CF and SSD), after I'm done installing DOS and reboots, computer stops right after POST with a blinking prompt when it's supposed to boot MS-DOS.
Currently I'm stuck with having to run DOS off an old HDD and use the CF/SSD as data disks, which is not so bad in itself but I'd still rather get rid of the old HDD if possible.

Is there anything I missed in BIOS or another limit I am not aware of?

If that helps it's a 486DX2-66 with a Soyo SY-025K2 motherboard. I already flashed the latest BIOS I could find.
BIOS is Award 4.50G.

Cheers!

Reply 1 of 5, by jmarsh

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Sounds like the devices were partitioned/formatted with different C/H/S values than the ones currently set in the BIOS.

Reply 2 of 5, by ultimate386

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jmarsh wrote on 2020-02-15, 19:00:

Sounds like the devices were partitioned/formatted with different C/H/S values than the ones currently set in the BIOS.

Agreed. Might also give fdisk /mbr a try.

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Reply 3 of 5, by derSammler

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I have that issue with DOMs that are smaller than 504 MB but auto-detected with LBA addressing, even though they require CHS addressing. With LBA, I can access all data on them but they won't boot, so I have to change LBA to Normal (CHS) in the BIOS to make them work.

How large were the CF card(s) and SSD you tested? Even if the BIOS supports LBA, it may simply not be able to work correctly with larger drives.

Reply 4 of 5, by jmarsh

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ultimate386 wrote on 2020-02-15, 19:26:

Agreed. Might also give fdisk /mbr a try.

Can't rely on that because later versions of fdisk only replace the boot code and leave the partition table untouched.

Reply 5 of 5, by Boohyaka

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jmarsh wrote on 2020-02-15, 19:00:

Sounds like the devices were partitioned/formatted with different C/H/S values than the ones currently set in the BIOS.

How would I check that, and how would I do that in the first place? 😀 Here's what I did:
- Go in BIOS, auto-detect HDD, pick "correct" settings
- Boot on floppy, fdisk a primary DOS partition
- Boot on 6.22 install disk, install DOS
- Reboot after install -> not booting

derSammler wrote on 2020-02-15, 19:44:

I have that issue with DOMs that are smaller than 504 MB but auto-detected with LBA addressing, even though they require CHS addressing. With LBA, I can access all data on them but they won't boot, so I have to change LBA to Normal (CHS) in the BIOS to make them work.

How large were the CF card(s) and SSD you tested? Even if the BIOS supports LBA, it may simply not be able to work correctly with larger drives.

CF card is 2GB and setup as "NORMAL" (non-LBA) in BIOS.
SSD is 128GB, 8GB detected in BIOS with LBA, 1 extended partition with 4 logical drives (3x2GB+1x1.8GB)

ultimate386 wrote on 2020-02-15, 19:26:

Agreed. Might also give fdisk /mbr a try.

Interestingly, looks like it did the trick, thank you! I did exactly what I explained above, then did a fdisk /mbr then reboot, it's now booting in DOS6.22 from the CF and reporting the correct size.
That's funny, fdisk /mbr has always been a command I've been told not to use because dangerous, particularly when dealing with LBA (not the case with CF, though).
I'll play with it some more, thank you 😀

jmarsh wrote on 2020-02-15, 20:19:

Can't rely on that because later versions of fdisk only replace the boot code and leave the partition table untouched.

Looks like it's ok though, is there anything I can do to make sure I'm good to go?
Thanks all

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