IBM RT PC Options Installation page 73

TNL SN20-9864 (May 1987) to 75X0217
7. Connect E on the cable to the 34-pin connector on the rear of the
new fixed-disk drive. Connect E 1 to the 20-pin connector on
the drive.
Connector
(20-Pin)
Signal
Connector
(34-Pin)
8. If you are installing R40 or R70 fixed-disk drives, route the
2-34 Options Installation
fixed-disk and diskette drive second cable bundle around and in front
of the power supply.