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I am trying to repurpose an old Acer Aspire M1641 to copy/format bulks of 3.5'' floppy disks. I think it's one of the last generations of computers to have a 34 pin floppy disk drive header as it also has SATA headers.

I have two working 3.5'' floppy drives, a floppy drive 34 pin cable connector with three ends (one for the motherboard, and two for A: and B: drives) and the motherboard has a 34 pin header.

I have connected the two drives to the motherboard's 34 pin header using the cable connector. I also connected the two drive's 4 pin power connectors.

When I boot and check the BIOS, I only have option for "Drive A:", there are no options for a "Drive B:". Windows only shows one of the two floppy drives, even if the second one seems to work (It seems like the drive takes the disk and spins it).

I tried changing the cable connector and changing the way it was connected but it was no use. I also tried other floppy drives and it did the same.

I couldn't find any specifications sheet about the computer's motherboard that told that there where only support for one floppy drive.

How can I get both floppy disk drives to work? Does the Acer Aspire M1641 motherboard supports two floppy disk drives?

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    As a workaround you can use a USB floppy drive as your second drive. Shouldn't be too hard to find and they're not that expensive. This is assuming your disks are either standard 720K or 1440K MS-DOS format floppies, otherwise the USB controller might not recognize them. – Ross Ridge Sep 9 '16 at 7:18
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Unfortunately, you can't connect two floppy drives to the motherboard header on that system. Like most motherboards since sometime around 2002–2003, it only supports one floppy drive, probably because its I/O is implemented using a low-pin-count SuperIO chip with too few pins to drive two floppy drives. The fact that your BIOS setup only mentions one floppy drive is a dead giveaway.

Since you're copying 3.5" floppies, you have a few possible solutions:

  • if you're only copying standard DOS floppies, an external 3.5" USB drive would work;
  • if you're copying more complex floppies, you could use something like a Kryoflux (with both drives connected to it).
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On modern motherboards, the floppy is controlled by the Super I/O chip, and often this chip is only capable of controlling one floppy drive, because the additional drive select/moter pins are not present by design.

I have a similar problem: My motherboard has a Nuvoton NCT6776F Super I/O chip, and that can work with one floppy only.

I am thinking of connecting some lines on the parallel port header to the missing lines in the floppy cable to be able to add a second drive (actually, while I'm at it, I could add a second cable and use 4 drives, 2x 5.25" and 2x 3.5" ...), but I haven't done so yet, so I don't know if it will work. I will also need to modify the drivers (easy on Linux, or even Freedos ...).

To verify your Super I/O chip can only work with one drive, please look at the motherboard and find out exactly what type it is. I tried to google for it, but apparently there are several models, and Acer uses different motherboards. Very likely it's MSI board. If you know the motherboard, you can try to look up which chips it uses.

Alternatively, on this picture of an Acer M1641 motherboard you can see the Super I/O chip on the top right. So you can try to find the datasheet for it directly using the number on it. With the datasheet, it's possible to find out exactly if it supports only one floppy, or several floppies.

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    A few years ago I was tempted to add a toggle switch connected inline to the floppy cable, but I never got round to it — that motherboard died and my current main system can't control any floppy drives at all. Adding a hardware switch would avoid needing to modify the drivers, but only one drive would be usable at a time... – Stephen Kitt Sep 8 '16 at 7:27
  • How can you add an hardware toggle switch to switch between the two drives? I guess you could do it by routing the power only to one of them but I'm not sure it would even work. How can you do so? – user2109 Sep 8 '16 at 17:46
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    @user2109: Look at the pinout. You'll have to switch /MOTA between /MOTA and /MOTB and /DRVSA between /DRVSA and /DRVSB. Yes, it will work (that's exactly what the controller does), but for your purpose copying to hard disk and then inserting the second disk is maybe less work then having to press a switch. – dirkt Sep 9 '16 at 5:13
  • @user2109 - following up on dirkt's comment, using a DPDT switch for /MOTA | /MOTB + /DRVSA | /DRVSB would make more sense if you were trying to use both a 3.5 inch floppy drive and a 5.25 inch floppy drive on the same system (but not at the same time). I have the side covers off my PC, so in the rare instances when I want to use a 5.25 inch floppy drive, I unplug the 3.5 inch drive and plug in the 5.25 inch drive. I still needed a dual connector cable, since the 5.25 inch drive uses a card edge connector, while the 3.5 inch floppy uses a pin connector. – rcgldr Jul 6 '18 at 4:13
  • I used to do something similar, but (IIRC -- it was a long time ago) I think I had one size floppy drive inside the case (probably 3.5"), and an external connection that could be switched between the other sized floppy or a tape-backup unit. – TripeHound Jul 12 '18 at 9:32
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Back in the day, it was VERY common to encounter an IBM compatible which had only a single floppy drive, invariably designated as drive A.

Do you imagine it phased us? :)

The solution was dead easy. You inserted the floppy in drive A and issued the DOS command COPY A: B: which resulted in the system prompting the user to swap disks. It read disk 1 from A:, then paused awaiting user-interaction, then wrote back to disk 2 in A: (i.e. it thought the floppy drive was now B: ).

Only expensive models had two floppy drives. No one wanted to pay for two, since the above solution was dead easy on the cheaper single-drive models.

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