SCSI-3 from FOLDOC

SCSI-3

An ongoing standardisation effort to extend the capabilities of SCSI-2. SCSI-3's goals are more devices on a bus (up to 32); faster data transfer; greater distances between devices (longer cables); more device classes and command sets; structured documentation; and a structured protocol model. In SCSI-2, data transmission is parallel (8, 16 or 32 bit wide). This gets increasingly difficult with higher data rates and longer cables because of varying signal delays on different wires. Furthermore, wiring cost and drive power increases with wider data words and higher speed. This has triggered the move to serial interfacing in SCSI-3. By embedding clock information into a serial data stream signal delay problems are eliminated. Driving a single signal also consumes less driving power and reduces connector cost and size. To allow for backward compatibility and for added flexibility SCSI-3 allows the use of several different transport mechanisms, some serial and some parallel. The software protocol and command set is the same for each transport. This leads to a layered protocol definition similar to definitions found in networking. SCSI-3 is therefore in fact the sum of a number of separate standards which are defined by separate groups. These standards and groups are currently:

 X3T9.2/91-13R2 SCSI-3 Generic Packetized Protocol
 X3T9.2/92-141 SCSI-3 Queuing Model
 X3T9.2/92-079 SCSI-3 Architecture Model
 IEEE P1394 High Performance Serial Bus
 X3T9.2/92-106 SCSI-3 Block Commands
 X3T9.2/91-189 SCSI-3 Serial Bus Protocol
 X3T9.2/92-105 SCSI-3 SCSI-3 Core Commands
 	 SCSI-3 Common Command Set
 X3T9.2/92-108 SCSI-3 Graphic Commands
 X3T9.2/92-109 SCSI-3 Medium Changer Commands
 X3T9.2/91-11 SCSI-3 Interlocked Protocol
 X3T9.2/91-10 SCSI-3 Parallel Interface
 X3T9.2/92-107 SCSI-3 Stream Commands
 	 SCSI-3 Scanner Commands

Additional Documents for the Fibre Channel are also meant to be included in the SCSI-3 framework, i.e.:

 	 Fibre Channel SCSI Mapping
 	 Fibre Channel Fabric Requirements
 	 Fibre Channel Low Cost Topologies
 X3T9.3/92-007 Fibre Channel Physical and Signalling Interface
 	 Fibre Channel Single Byte Commands
 	 Fibre Channel Cross Point Switch Topology
 X3T9.2/92-103 SCSI-3 Fibre Channel Protocol (GPP & SBP)

As all of this is an ongoing effort of considerable complexity, document structure and workgroups may change. No final standard is issued yet. In the meantime a group of manufacturers have proposed an extension of SCSI-2 called Ultra-SCSI which doubles the transfer speed of Fast-SCSI to give 20MByte/s on an 8 bit connection and 40MByte/s on a 16-bit connection. [Hermann Strass: "SCSI-Bus erfolgreich anwenden", Franzis-Verlag Muenchen 1993].

Last updated: 1995年04月19日

Nearby terms:

SCSI-1 ♦ SCSI-2 ♦ SCSI-3 ♦ SCSI adapter ♦ SCSI adaptor ♦ SCSI controller

Try this search on Wikipedia, Wiktionary, Google, OneLook.