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Drive letter assignments

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Syntho

Experienced Member
Joined
Feb 23, 2022
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My 386 has a bios from 1991. I believe there is a way to switch floppy drive letter assignments on later bios versions but mine doesn’t have it. I have a 3.5” and a 5.25” drive. I want the 3.5” to be A: and the 5.25” to be B:.

The problem is that the way it’s hooked up now works, but the drive letters are reversed, against my liking, and switching the location of the connectors on the cable itself makes both drives not work at all.

I’ve never encountered this before. The middle portion of the cable has the connectors for the 3.5” and 5.25” drives and so does the end of it. Right now I’m using the 3.5” connector in the middle of the cable and the 5.25” one on the end of it. That’s the only combo that gets the drives working.

Is there a way to manually change the drive letters somebody?
 
Build your own cable, if the stock one doesn't work. Any other way and you'll be the victim of software that talks directly to the hardware or BIOS. I'm assuming that you want to change the boot drive unit.
 
Yeah, it’s that, combined with the fact that I’m just picky and have always had A: as my 3.5” drive :)

I guess there’s nothing I can do except get a new cable. I’ve never made my own before.
 
Do you have any guess why it wouldn’t work when I switch locations on the cable? I think I might just buy one first instead of making one. But I’m worried since if the one I have doesn’t work, will another one just like it? Hmm.
 
Syntho said:
[...] and switching the location of the connectors on the cable itself makes both drives not work at all.

I’ve never encountered this before.
Click to expand...
That is actually normal behaviour. Your 5.25" drive most likly has the terminator installed/enabled and as such, it will not work in the middle of the cable. The terminator can be physical or a jumper, depending on the drive's age. Remove it and it should work.
 
It’s a TEAC FD-55GFR. See the photo for the current jumper settings: https://ibb.co/2NBXGRF

Reading the manual, hope I spot what to do. One jumper is on the D1 setting.
 
I’m confused. The 5.25” drive is on D1, and the 3.5” (TEAC FD-235HF 3240) has a jumper set on DS1 if I’m reading this right. The 5.25” drive’s manual says to keep the twisted end on the A drive and the B drive on the untwisted one (which is in the middle). I’ve done just that with no luck.
 
Hey guys, never mind. I stumbled upon some magic combination and it’s working now. Don’t know what I did differently since I thought I had it like this before but it’s fine now.
 
Timo W. said:
That is actually normal behaviour. Your 5.25" drive most likly has the terminator installed/enabled and as such, it will not work in the middle of the cable. The terminator can be physical or a jumper, depending on the drive's age. Remove it and it should work.
Click to expand...
On the short runs involved in a PC, it doesn't matter which drive has the termination enabled--it is sufficient that at least one of them does, because a pullup on host-to-device signalling lines is required (OC drive). If you/re looking at a half-meter long cable max, the issues with crosstalk and reflection are minimal at floppy signalling speeds. As a matter of fact, the dedicated termination is largely absent on 3.5" drives--a higher-value pullup (2K-10Kohm) is used instead.
However, if you have more than one 5.25" drive with 150 ohm termination/pullups, it's important that only a single one have the pullups enabled. With two 150 ohm pullups on each line, the current required of the driver IC is in excess of 50 ma.
 
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Off topic: my TEAC FD-55GFR didn't come with a top or bottom plate to cover the internals. I looked online and apparently none of the others have tops or bottoms either, even though I see some screw holes for what looks like cover plates. Won't this get dust in the drive? I've got some laminating sheets and I could probably build a makeshift clear case for it to prevent dust. But if it were really going to be an issue, wouldn't they have made them with covers? Hmm.
 
I suspect that what you're seeing as screw holes for a bottom plate are the holes for the optional bottom-mounting of the drive. Many modern hard drives feature this as well.

It's sort of silly to cover the internals, when you have dust being sucked into the drive via the disk slot. Many 3.5" drives are better in this respect, using a shutter on the disk opening when no disk is present.
 
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