It’s kind of an elegant hack IBM did to make floppy drives easier to bother with.
Floppy drives were designed to attach to the computer in a bus topology, sharing all of their data connections. The only wires that weren’t in common were the Motor Enable and Drive Select lines, which is how the computer would tell the drives which one it wanted to talk to. This meant the drive needed to know which drive it was, so there were jumpers on the back so you could set them up as Drive 0 or 1 (which would show up in DOS as A or B). By twisting seven cables (three of which were ground and weren’t effected) and jumpering all drives as Drive 1(B), drives attached before the twist would respond as drive B and after the twist as drive A. That way you didn’t need to fuck with the jumpers. Some later drives even did away with the jumpers and hard wired them as B.
I’m not 100% sure off the top of my head, but the end result is that the drive is set to A: rather than B: in Windows. Something to do with the pins on the motherboard specifying the drive order.
Right the jumpers would be cable select, master , slave generally. You could use master and slave or cs but shouldn’t together. Not that you can’t but screwing up your jumpers was the easy way to be pulling you hair out for failure to boot to the right drive or failure to id in the right order.
Now I’m curious, why *does *the floppy drives cable have a little twist in it?
It’s kind of an elegant hack IBM did to make floppy drives easier to bother with.
Floppy drives were designed to attach to the computer in a bus topology, sharing all of their data connections. The only wires that weren’t in common were the Motor Enable and Drive Select lines, which is how the computer would tell the drives which one it wanted to talk to. This meant the drive needed to know which drive it was, so there were jumpers on the back so you could set them up as Drive 0 or 1 (which would show up in DOS as A or B). By twisting seven cables (three of which were ground and weren’t effected) and jumpering all drives as Drive 1(B), drives attached before the twist would respond as drive B and after the twist as drive A. That way you didn’t need to fuck with the jumpers. Some later drives even did away with the jumpers and hard wired them as B.
Thnx for this exposition!
I’m not 100% sure off the top of my head, but the end result is that the drive is set to A: rather than B: in Windows. Something to do with the pins on the motherboard specifying the drive order.
You are correct. Later drives sometimes had a cable select dip switch/pin or different ports on the motherboard.
Right the jumpers would be cable select, master , slave generally. You could use master and slave or cs but shouldn’t together. Not that you can’t but screwing up your jumpers was the easy way to be pulling you hair out for failure to boot to the right drive or failure to id in the right order.