A maximum data throughput of 20 Mbytes/sec for Narrow (8-bit) SCSI is offered by Ultra SCSI. Ultra Wide SCSI is a 16-bit version of the above that offers 40 Mbytes/sec of data transfer. It has a maximum cable length of 1.5 m (5 ft) with over 4 active IDs and 3 m (10 ft) with 4 or fewer active IDs. Ultra Wide differential SCSI has a maximum cable length of 25 m (82 ft).
Wide Ultra SCSI
Data transfer of 40 megabytes per second was first defined in SCSI Fast-20 mentioned below. It defines how it is used in the different generations of the SCSI standards.
SCSI Fast-20
This is characterized by 16 bit SCSI asynchronous commands with synchronous data transfer rates of up to 40 megabytes per second.
