A brief write up on SCSI
SCSI stands for Small Computer Systems Interface and was formulated in 1986. Peripherals like disk drives require an I/O interface that provides room for increasing bandwidth. The original SCSI-1 standard provides a clock speed of 5MHz and a 5MB/second buffer-to-host data transfer rate through an 8-bit wide bus.
SCSI-2 provides new command sets and doubles the clock speed to 10MHz and the data transfer rate to 10MB/second through an 8-bit bus. Combined with a wider 16-bit bus and Fast SCSI capabilities, which allow synchronous data transfers, SCSI-2 increases the original buffer-to-host data transfer rate by a factor of four to 20MB/second.
The Ultra SCSI or SCSI-3 increases the clock speed to 20MHz while keeping the bus widths the same: narrow Ultra SCSI provides a data transfer rate of 20MB/second through a 8-bit bus and Wide Ultra SCSI provides a data transfer rate of 40MB/second through a 16-bit bus. The latest Ultra2 SCSI provides a data transfer rate of 40MB/second through a 8-bit bus and 80MB/second through a 16-bit bus.
As with all computing, faster and newer standards are emerging and SCSI will continue to evolve and provide even faster throughput in the future.