I have never
seen a 'real' GPIB cable with anything other than the
 double-sided connectors and jackscrews. So I wonder what cables this
 was designed to be used with. Who made it?  
 I don't recall the brand, but it was a disk drive.  I seem to recall
 that the command set was only "sort of" HPIB; i.e. "interesting"
 extensions. 
 
As far as I am aware, there is no stnadard command set for
HPIB/GPIB/IEEE-488 disk drives. There are 4 that I know of, and probably
many others (HP used 3 command sets : Amigo, SS/80 and CS/80, and hten
there were the Comoodore drives for the PET).
  I never played much with it, just had it around for a
time as a
 curiosity item.  
If thios was supposedly an HP-drive compatible device, it would be
interesting to find out what it was.
-tony