SCSI-1 was the first implementation of SCSI and was officially known as ANSI X3.131-1986. The major features of SCSI-1 are as follows:
8-bit parallel bus
5MHz asynchronous or synchronous operation
4MBps (asynchronous) or 5MBps (synchronous) throughput
50-pin cables with low-density pin-header internal and Centronics-style external connectors
Single-ended (SE) unbalanced transmission
Passive termination
Optional bus parity
SCSI-1 is now considered obsolete; in fact, the standard has been withdrawn by ANSI and replaced by SCSI-2.