This rack-mount disk drive appears to have come out of a paging system.

It is labeled "Subscriber Memory Backup" from a Virginia-based company called Commonwealth Communications Industries, Ltd. The model number is apparently OP-635.

The unit has a standard 3-prong AC power cord, a keyed 4-pin female power connector, and a 50-pin ribbon cable with a dual row female connector.

The drive controller electronics are located underneath the drive mechanism.