IBM 704 - Manual (Page 188)

Installing Internal Drives
9. Connect a signal cable 1 to the back of the drive. If a narrow
SCSI cable is already connected to devices in the 5.25-inch drive
bays, add your drive to the cable. Otherwise, install a standard
50-pin ribbon cable: connect this cable to connector J8 (on the
lower backplane for the 5.25-inch drive bays) and to the drive.
10. Connect a power cable 2 to the back of the drive. Power
cables for removable-media drives come with your server. The
connectors are keyed and can be inserted only one way.
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170 PC Server 704 User's Handbook