I've tried get four floppy drives going in a system before, so here are some things I learned:

• A floppy controller uses I/O addresses, an IRQ and a DMA channel. Two floppy controllers on the same I/O address will absolutely conflict, as there's no way to talk to only one controller or the other, you'd be talking to both at the same time.
• Some floppy controllers have a jumper that can select a secondary I/O address, but these don't usually change the IRQ or DMA.
• In theory the IRQ and DMA can be shared if only one drive is used at a time, however I was never able to get this to work (the drive lights would come on but the system would freeze).
• You need special BIOS support for a floppy controller on the secondary I/O channel. I found a handful online and flashed them as ROMs on a NIC, and a few of them made the drive LEDs come on but none were successful. I thought a BIOS that supported two controllers might allow sharing of the IRQ/DMA between cards but apparently not.
• The PC originally supported up to four drives on a single controller. It had an internal connector for two internal drives, and an external connector for two external drives. Early BIOSes supported four drives, but I think later ones (with onboard controllers) only support what their onboard controller can do.
• You can get some very rare ISA floppy controllers that appear to the system as a single controller, but they have two floppy connectors on them and allow up to four drives to be used. Typically they come with their own BIOS so that DOS can see the extra drives. I guess DRIVER.SYS is still needed but haven't had a chance to investigate since I got hold of a four-drive controller.

If your question is more about replacing the onboard controller with your ISA one, here are some tips:

• You will need to disable the onboard controller in the BIOS (or set it to auto so it disables itself automatically) otherwise you'll get the conflict mentioned above.
• ISA controller cards like the one in your photo don't have a BIOS, they rely on the system BIOS for support. If your system BIOS only supports one floppy drive, then you'll only get one regardless of whether you use the onboard or ISA controller.
• Find out what your onboard floppy controller is. Chances are the hardware supports two drives, it's the BIOS that doesn't bother with the second one. You might be able to get away with using DRIVER.SYS which I believe may talk to the controller directly - not sure about this though, you'd think that would conflict with the BIOS-controlled drive.

If you get it to work (or even if you don't), post an update with what you tried. I've never tried to get two drives working on a BIOS that only supports a single drive, so I'm interested to know whether it's possible.

I had no problems getting 4 floppy drives working using an Adaptec AHA-1542CF. That one has a floppy controller which can be set to a secondary i/o address. It will most likely not work with such cheap multi i/o conrollers.

Does the Adaptec have a BIOS that supports the secondary I/O? All the cards I have are multi I/O controllers with no BIOS unfortunately.

Yes. That's where you actually set the i/o address.

I've got an old 286 (w/ onboard FDC) that refuses to work with multi-i/o cards with built-in IDE+FDC controllers.
Disabling the FDC portion via jumper has no effect. The internal floppy controller would nolonger function,
as long as such cards are installed. If I remove them, the system instantly workes normal again.
Installing an stand-alone IDE control.. err -host interface- card works, though. 😀

Do you know what kind of FDC the 286 has? Perhaps it's a nonstandard one? I seem to recall there being a few different variants, although I don't think I've ever seen one that's outright incompatible with the one introduced on the first PCs.

Yes, it is a WD37C658JM.

Interesting. According to the datasheet it's BIOS compatible with standard PCs, so it would seem that your BIOS would be capable of talking to the controller on other I/O cards. How strange that it doesn't work!

I apologize, I meant it in reverse. Should have been more precise about this. 😊
I wanted to disable the external FDC portion on the multi-i/o card, so I could keep the internal FDC working..
Alas, it didn't work. Disabling the FDC portion on the ISA card had no effect.

I did thsi, because I required the IDE part on the i/o card.
My workaround was to use XT-IDE Universal BIOS and a simple IDE CD-ROM card.

Luckily, it had a setting for primay-master/-slave also. If it hadn't, XT-IDE would have been my last hope to boot from 2nd IDE.
- Most models of such cheap ISA CD-ROM cards only have an option for secondary-master/-slave.

Oh I see, sorry for misunderstanding.

That is still odd though, it seems the I/O controller didn't fully disable the floppy part. I had some issues once trying to get a PnP sound card's IDE interface working as the PnP manager said the I/O address was conflicting with the floppy controller. Looking at the end of this I/O map it seems that the floppy controller's I/O addresses actually overlap with those of the primary IDE controller.

The floppy controller seems to use 0x3F2, 0x3F4 and 0x3F5 while the IDE primary slave uses 0x3F6 and 0x3F7. Perhaps these addresses are close enough together that the primary IDE interface and floppy controller must reside on the same card in order for it to work? Perhaps the cheaper I/O cards don't fully decode the I/O port addresses so still respond to the floppy controller I/O ports when only the primary IDE controller is active.

derSammler wrote on 2017-10-08, 08:09:

I had no problems getting 4 floppy drives working using an Adaptec AHA-1542CF. That one has a floppy controller which can be set to a secondary i/o address. It will most likely not work with such cheap multi i/o conrollers.

Did you du this while having a bios that only supports two drives?
if so how did you proceed?

zapedge wrote on 2021-02-02, 14:21:

derSammler wrote on 2017-10-08, 08:09:

I had no problems getting 4 floppy drives working using an Adaptec AHA-1542CF. That one has a floppy controller which can be set to a secondary i/o address. It will most likely not work with such cheap multi i/o conrollers.

Did you du this while having a bios that only supports two drives?
if so how did you proceed?

http://www.vcfed.org/forum/showthread.p ... post615458

I’ve run a io card like that before on a mobo that already had one. I don’t recall any issues. It just seemed to work fine.

Sphere478 wrote on 2021-02-03, 15:20:

I’ve run a io card like that before on a mobo that already had one. I don’t recall any issues. It just seemed to work fine.

Did you have to load any additioanl drivers? And how did you set up the drive types on the additional controller?

Bondi wrote on 2021-02-03, 16:51:

Sphere478 wrote on 2021-02-03, 15:20:

I’ve run a io card like that before on a mobo that already had one. I don’t recall any issues. It just seemed to work fine.

Did you have to load any additioanl drivers? And how did you set up the drive types on the additional controller?

no it was very plug and go, I was using it in windows.