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].

   (1995-04-19)