Table of SCSI Terminology

SCSI Terminology

STA-Endorsed Terminology for SCSI Parallel Interface Technology

STA Terms Bus Speed,
Mbytes/Sec,
Max Bus
Width,
Bits Max. Bus Length, Meters ⁽¹⁾ Max. Device
Support

Single-
ended Diff. LVD

SCSI-1 ⁽²⁾ 5 8 6 25 ⁽³⁾ 8

Fast SCSI ⁽²⁾ 10 8 3 25 ⁽³⁾ 8

Fast Wide SCSI 20 16 3 25 ⁽³⁾ 16

Ultra SCSI ⁽²⁾ 20 8 1.5 25 ⁽³⁾ 8

Ultra SCSI ⁽²⁾ 20 8 3 25 ⁽³⁾ 4

Wide Ultra SCSI 40 16 - 25 ⁽³⁾ 16

Wide Ultra SCSI 40 16 1.5 - - 8

Wide Ultra SCSI 40 16 3 - - 4
Ultra2 SCSI ^(2,4) 40 8 ⁽⁴⁾ 25 12 8

Wide Ultra2 SCSI ⁽⁴⁾ 80 16 ⁽⁴⁾ 25 12 16

STA Terms	Bus Speed, Mbytes/Sec, Max	Bus Width, Bits	Max. Bus Length, Meters ⁽¹⁾	Max. Device Support
Single- ended	Diff.	LVD
SCSI-1 ⁽²⁾	5	8	6	25	⁽³⁾	8
Fast SCSI ⁽²⁾	10	8	3	25	⁽³⁾	8
Fast Wide SCSI	20	16	3	25	⁽³⁾	16
Ultra SCSI ⁽²⁾	20	8	1.5	25	⁽³⁾	8
Ultra SCSI ⁽²⁾	20	8	3	25	⁽³⁾	4
Wide Ultra SCSI	40	16	-	25	⁽³⁾	16
Wide Ultra SCSI	40	16	1.5	-	-	8
Wide Ultra SCSI	40	16	3	-	-	4
Ultra2 SCSI ^(2,4)	40	8	⁽⁴⁾	25	12	8
Wide Ultra2 SCSI ⁽⁴⁾	80	16	⁽⁴⁾	25	12	16

Notes:
⁽¹⁾ The listed maximum bus lengths may be exceeded in point-to-point and engineered applications.
⁽²⁾ Use of the word "narrow", preceding SCSI, Ultra SCSI, or Ultra2 SCSI is optional.
⁽³⁾ LVD was not defined in the original SCSI standards for this speed. If all devices on the bus support LVD, then 12-meter operation is possible at this speed. However, if any device on the bus is single-ended only, then the entire bus switches to single-ended mode and the distances in the single-ended column apply.
⁽⁴⁾ Single-ended is not defined at Ultra2 speeds.

This chart comes from an article by the same name published for the STA in the May 1996 issue of Computer Technology Review. The terminology was standardized through the joint efforts of the T10 Technical Committee on SCSI and the SCSI Trade Association. The chart was updated 8/13/1998.