Greetings Time-travellers,

I have a Gigabyte GA-8VM800M-775 motherboard from ~2005 that I've successfully been using as a DOS/98SE/XP retro machine. Recently I installed a second floppy drive into the case only to rediscover disappointingly that the BIOS only supports one floppy drive (only A: and not B:).

Looking for a solution to enable 2 floppy drives I came across a video, **Installing 2nd Floppy on unsupported motherboard** which shows editing CMOS to enable a second floppy https://www.youtube.com/watch?v=z9YXyfG0Vf0

I performed the edits on my CMOS using RWEverything http://rweverything.com/, but when I reboot, the least significant 4 bits of 0x10h always resets to 00 (erasing the config for the B: drive), but the other modified bytes keep their changes.

Does anyone know what is going on or have suggestions?

I have read that the missing option for a second floppy is a pure BIOS limitation and can be patched, so I had hoped that this modifcation may work for my motherboard. The SuperIO chip on the motherboard is a Winbond W83627EHF (https://pdf1.alldatasheet.com/datasheet-pdf/v … /W83627EHF.html) that supports multiple floppy drives according to the datasheet, but I do not know if the circuitry of the GA-8VM800M-775 motherboard supports drive B: or not, and I will need to remove the motherboard to test that.

Per some recommendations about this issue on another thread here (Intel 815e Chipset Motherboard Shows Only One Floppy Drive) I booted a live install of Linux (Ubuntu) but could not access/detect a second floppy drive. I also configured and attempted to access B: with ANADISK as described at http://www.seasip.info/VintagePC/floppies.html but could not access B:
* The first floppy is accessible under DOS as both A: & B: but only accessible in ANADISK as A:
* After toggling bit 4 of F0h of the SIO FDC (Swap Drive 0, 1 according to the SIO chip datasheet) I could not access either drive under DOS (though ANADISK could now access the first floppy as B:).

I'd like to get this mobo supporting two floppy drives if possible (a 3.5" & 5.25"), because aside from this problem with not supporting two floppy drives, and despite not having an Intel 865 chipset it's proven to be the perfect "Time Machine" PC.

Questions bouncing around:
* Has this kind of CMOS modification to enable a second floppy drive worked for anyone here with other motherboards?
* What's causing the least significant 4 bits of 0x10h to reset and is it possible to modify the BIOS so that it will not reset them?
* What's the best way to check whether the hardware can support two floppy drives?
* Without resorting to USB or PCI floppy drive controllers (which I do not want in this case) are there any other tricks for installing 2 floppy drives with BIOS that only support one?.
* Is the fact that linux / ANADISK did not detect a second drive conclusive proof that the hardware does not support it?

Perhaps I should ask this question on a BIOS modding forum, but as the computer is quite retro and my question involves floppy drives, I thought I would ask my favourite android 😀

Thanks in advance for any thoughts on the above!

Perhaps I need to remove ithe motherboard from the case to probe the the circuitry for continuity between drive select B pin and the SIO chip.. hmm... Suggestions for which pins to test for continuity to test whether the motherboard can physically support 2 drives could be helpful too, if anyone knows!