# SCSI Information

## Background

It all started back in 1979 when the diskdrive manufacturer come with the bright idea to make a new transfer protocol. The protocol was named Shugart Associates Systems Interface, SASI. This protocol wasn't an ANSI standard, so NCR join Shugart and the ANSI committee X3T9.2 was formed. The new name for the protocol was, Small Computer Systems Interface, SCSI.

Common Command Set, CCS, was added in 1985. ANSI finished the SCSI standard in 1986. SCSI-II devices was released in 1988 and was an official standard in 1994. SCSI-III is currently not yet official.

## Usage

SCSI is used to connect peripherals to an computer. It allows you to connect harddisks, tape devices, CD-ROMs, CD-R units, DVD, scanners, printers and many other devices. SCSI is in opposite to IDE/ATA very flexible. Today SCSI is most often used servers and other computers which require very good performance. IDE/ATA is more popular due to the fact that IDE/ATA devices tend to be cheaper.

## Definitions

### SCSI

Short for Small Computer Systems Interface. The original SCSI protocol. ANSI standard X3.131-1996. Busspeed 5 MHz. Datawidth 8 bits.

### SCSI-II

SCSI-II adds support for CD-ROM's, scanners and tapedrives.

### Fast SCSI-II

Uses the busspeed of 10MHz instead of the original 5MHz.

### Wide SCSI-II

Uses 16 bits instead of the original 8 bits.

### Ultra SCSI-III

Uses the busspeed of 20MHz.

Contributors: Joakim Ögren

Source:
From the head of Joakim Ögren

Copyright © The Hardware Book Team 1996-2001.
May be copied and redistributed, partially or in whole, as appropriate.
Document last modified: 2001-06-07