PC floppy cable twists...

[Jules Richardson]

Chuck Guzis wrote:
> On 10/20/2005 at 5:48 PM Jules Richardson wrote:
> 
> 
>>... discussion about this on another list got me curious - what *was* 
>>the point of that cable twist in a (IBM clone) PC floppy cable, when 
>>every other system on the planet was using straight-through cables?
> 
> 
> It's actually pretty simple--there's only a single "motor on" line for the
> standard floppy pinout.  IBM wanted to control drive motors individually.
> The only ways to do that are with individual drive cables or using the
> "twist" (or some modification of it) so that the individual drive motor
> enables are given different conductors in the cable.

Brilliant - most informative, thanks :) (although I've seen mention of 
the hack-like nature of the cable twist on this list before, I don't 
remember anyone ever saying why it was done!)

That does beg the question of whether there's any other jumpering to 
worry about when putting a PC-setup floppy onto a classic system (other 
than getting the drive select jumpering right).

cheers

Jules