If you mess around with old PCs, you’ll need to know how to find IDE pin 1 and floppy pin 1 on old drives. Sometimes there will be a mark by pin 1. The connector should even be keyed so you can’t insert the connector upside down. Usually it’s one or the other, but sometimes it’s neither.
Typically a red stripe indicates pin 1 on the cable side, and either a silk screened indicator or a square solder joint on the connector side.
What happens when you plug the cable in wrong
Systems act goofy if you plug the IDE connector in wrong. Sometimes they just give you a black screen at power-up. Sometimes they fail to detect the drive. A floppy drive should just fail to operate if you connect it wrong, but in extreme cases, where someone misaligned it really badly, I did see it ruin drives.
This is one reason manufacturers started keying cables. If you have a keyed cable and it doesn’t fit, here’s how to modify it to fit as long as you’re willing to be careful.
Find IDE pin 1 and floppy pin 1
So here’s the trick. Pin 1 on your cable should always have a red stripe on it. If yours doesn’t, think about replacing the cable. Seriously. On IDE hard drives and CD-ROM drives, the red stripe goes on the side facing the power connector.
And on floppy drives, it’s the opposite. The red stripe goes on the side away from the power connector. Why? Probably for the same reason that PCs use imperial 6-32 screws to secure cards in expansion slots and metric M3 screws to secure floppy and CD-ROM drives in drive bays. Standardize, schmandardize.
On the motherboard side, there should be an indicator next to pin 1. Frequently, too, pin 1 has a square solder joint while the rest of the pins have round solder joints. So look for the square solder joint if you can’t find a marking. The red stripe goes on pin 1.
If the cable and the connector are both keyed, then you can’t plug it in the wrong way. But sometimes the connectors weren’t keyed, to save costs. If the connector is keyed but the cable isn’t, I recommend you replace the cable. It cuts down on possible mistakes.
And that’s it. That’s how you find IDE pin 1 and floppy pin 1.
A trick for replacing cables
Newer 80-conductor UDMA cables are backward compatible with the older 40-conductor IDE cables. So you can use the newer cable in an older computer if you need to. Using an older 40-conductor cable in a system that came with an 80-conductor cable will still work, but it degrades performance. The 80-conductor cables tended to be higher quality, so using them can prevent or solve some weird issues.