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What Does SCSI-3 Mean?

Small Computer System Interface 3 (SCSI-3) is an ongoing standardization effort for extending the features of SCSI-2. The key goals of SCSI-3 include the following:

  • Additional devices on a bus (as many as 32)
  • Increased distances between devices (longer cables)
  • Speedy data transfer
  • More command sets and device classes
  • Structured protocol model
  • Structured documentation

Techopedia Explains SCSI-3

The SCSI-3 standard is a collection of other standards. These standards are arranged into a framework based on the SCSI-3 architecture documents. Used in several high-end systems, SCSI-3 often utilizes a MicroD 68-pin connector having thumbscrews. It is also referred to as Mini 68.

The most widely used bus width for SCSI-3 is 16 bits, with a transfer rate of 20 MBps.

In SCSI-2, data is transmitted in parallel (i.e., 8, 16 or 32 bits wide). This can get significantly challenging with longer cables and higher data rates owing to varying signal delays on various wires. In addition, drive power and wiring expenditure grow with higher speeds and wider data words. This has triggered the migration to serial interfacing in SCSI-3.

Issues with delay are eradicated by embedding clock information to serial data stream signals. Also, driving a single signal uses up less driving power and cuts down connector price and size.

In order to permit backward compatibility and increased flexibility, SCSI-3 permits the use of many different transport systems, some parallel and some serial. For every transport, the command set and software protocol are the same. This results in a layered protocol definition that is much like the definitions present in networking.

SCSI-3 therefore is the sum of quite a few independent standards that are based on independent groups.


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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.