Editing Digital Storage Systems Interconnect (section)

== Characteristics ==

The major characteristics of the DSSI bus are:
* Eight-bit data path
* Up to eight nodes on the bus including variable numbers of [[SCSI initiator and target|initiators]] and [[SCSI initiator and target|targets]]
* Distributed arbitration
* Peak bandwidth of 4 megabytes per second
* All systems connected to the same DSSI bus must have a common power/ground.
* "The [[Q-Bus]] 5-Enclosure Rule": For Q-bus VMScluster configurations, a  maximum of five enclosures, ''excluding'' SF200/210s, can be configured on a single DSSI bus. Note that only ''one'' (1) SF100 is allowed on any DSSI bus.
* "The [[VAX 6000]] Cabinet Rule": For a VAX 6000 DSSI VMScluster system, a maximum of two or three VAX 6000 systems and one storage cabinet, typically an SF200 or SF210, can be configured on a single DSSI bus.
* Maximum DSSI bus length  cannot exceed 27 meters (89 feet) and ground offset voltage cannot exceed 30mv (dc) or 10.5mv (rms).

                                  Bus Length      Allowable Offset
                            Meters/Feet  (DC) (AC)
                            -----------     ----------------
                            up to 20/65     200mv   70mv (rms)
                            20-25/65-82      40mv   14mv (rms)
            VAX6000 QUAD-Host--> 27/89      30mv   10.5mv (rms)
            VAX7000
            VAX10000