PC floppy cable twists...

Re: There are two stories on this one. Story 1 is that the original IBM power supply was only 63 watts, and didn't have enough power to run two drive motors at once. However, the "straight-through" interface only had one motor-control line, but several (3 or 4) drive select lines. By inserting the twist, one of the extra drive select lines became an independent motor on-off control line for the 2nd drive. Story 2 is that for service reasons, IBM did not want to have to deal with drive jumpering, they wanted every drive to be the same so that drives could be simply swapped with no fuss if one failed. I worked for Zenith [Data Systems] at the time, and Zenith [different division, but we had some contact after the IBM PC was introduced] made the original power supplies for IBM [as well as the power supply for my Z-100]. We were always told that story 1 was correct. Also, the logic behind story 2 doesn't address the fact that drive terminators still had to be configured. So I say it was because of the drive motor power requirements. That's my story, and I'm sticking to it.