SCSI Terms & Terminology

STA-Endorsed Terms & Terminology for SCSI Parallel Interface Technology

STA Terms
Bus Speed, MBytes/Sec. Max. Bus Width, bits
Max. Bus Lengths, Meters ⁽¹⁾
Max. Device Support

Single- ended LVD HVD

SCSI-1⁽²⁾ 5 8 6 ⁽³⁾ 25 8

Fast SCSI⁽²⁾ 10 8 3 ⁽³⁾ 25 8

Fast Wide SCSI 20 16 3 ⁽³⁾ 25 16

Ultra SCSI⁽²⁾ 20 8 1.5 ⁽³⁾ 25 8

Ultra SCSI⁽²⁾ 20 8 3 - - 4

Wide Ultra SCSI 40 16 - ⁽³⁾ 25 16

Wide Ultra SCSI 40 16 1.5 - - 8

Wide Ultra SCSI 40 16 3 - - 4

Ultra2 SCSI^(2,4) 40 8 ⁽⁴⁾ 12 25 8

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

Ultra3 SCSI or Ultra160 SCSI ⁽⁶⁾ 160 16 ⁽⁴⁾ 12 ⁽⁵⁾ 16

Ultra320 SCSI ⁽⁶⁾ 320 16 ⁽⁴⁾ 12 ⁽⁵⁾ 16

^Ultra640 640 16 ⁽⁴⁾ (7) ⁽⁵⁾ 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-meters operation is possible at this speed. However, if any device on the bus is singled-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 for speeds beyond Ultra.

(5) HVD (Differential) is not defined for speeds beyond Ultra2.

(6) After Ultra2 all new speeds are wide only.

SCSI Terms - STA overview of the different SCSI Standards and Cables.