The 9553A is a SCSI active terminator for "single-ended" SCSI bus subsystems.
Every SCSI system must have a terminator (technically, terminating resistors)
at each end of its internal and/or external bus. Typically one end will be a
motherboard or other control board, which has onboard termination. Terminators
like the 9553A are found at the other end of the bus, after all the devices.
The 9553A's Active Termination uses a sophisticated method of terminating the SCSI bus to
allow for faster speeds and longer cable lengths than could be possible otherwise.
This terminator is mounted on a DH68M (Micro-68 pin) connector.