PC floppy cable twists...

[Michael B. Brutman]

For the longest time I was stumped about how to get four drives onto a 
PC 5150.  The BIOS supports it, but looking at the cable it just 
shouldn't work.  There was the twist to control drive select and the one 
motor line - that's not enough to control four drives.

I started kicking myself really hard when I rememberd that the other two 
drives had to go on the external cable, which has it's own motor and 
drive select line ...

Still, mapping out the PC floppy cable compared to other systems was 
interesting.  Even compared to an AT it is different.  The AT supports a 
high density signal line on a previously unused pin.  The other systems 
looked like they had independent drive select lines, but as somebody 
else pointed out, the motors all ran at the same time.

With all of those pins on the interface, why wouldn't the motors be 
independently controlled?  That seems like a waste on any system, never 
mind the wear and tear on the drives & inserted floppies.


Mike