PC disk drive termination

Tony Duell ard at p850ug1.demon.co.uk
Thu Oct 20 19:26:14 CDT 2005


Somebody earlier claimed that IBM didn't bother with termination on the 
disk drives in the PC family.

I've just looked in the 'Hardware Maintenance and Service' manual for the 
PC/AT. This is the only HMS manual I have (I don't normally bother with 
boardswapper guides), but I would be suprised if the same principles 
didn't apply to the PC.

Anyway, the manual says : 

'Diskette Drive

o The terminating resistor must be installed on drive A (top unit).

o In a system unit with 2 diskette drives, remove the terminating resistor
  from drive B (bottom unit) for proper operation.

o The diskette drive end of the signal cable is attached to diskette 
  drive A.

Fixed disk drive 

o The terminating resistor must be installed on fixed disk drive C (left 
  unit)

o In a system unit with 2 fixed disk drives, remove the terminating resistor
  from fixed disk drive D (right unit) for proper operation '

There are diagramss showing the location of the terminating resistor pack on
the drive PCB that I can't sensibly reproduce in ASCII.

-tony




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