Digital Storage Systems Interconnect
The Digital Storage Systems Interconnect (usually given as DSSI) is a mass storage bus from DEC. It can also be used to create loosely-coupled multi-processors by sharing a number of disk drives between two systems. Such shared drives are termed 'Integrated Storage Elements' (ISEs).
DSSI made it possible to build VAXclusters from MicroVAX and smaller VAX computers by adding CI-bus functionality to smaller VAX systems.
Description from the 'Digital's Storage System Interconnect' protocol specification document:
"The DSSI, supporting the needs of low-end and mid-range systems, is one in a family of high-performance computer-to-computer interconnects (CI's) that combine a common host interface and port layer with an implementation-specific datalink and physical interconnect.
CI-class interconnects provide the transmission services required by Digital's Systems Communication Architecture (SCA) - a four-tiered set of protocols and interfaces as shown [to the right]."
The QBUS DSSI peripheral was the KFQSA. Some VAX CPU's had built-in DSSI peripherals, called 'Embedded DSSI Adapters' (EDAs); one such was the EDA640 included in the KA640 CPU of the MicroVAX 3300/3400. The VAX 4000 series also supported the DSSI via its CPU embedded adapter PDIA.
External Links
- DSSI - DSSI and related documents at Bitsavers
- Digital's Storage System Interconnect - protocol specification document
- MicroVAX Dual-Host Systems (EK-338AC-DH-003) - contains a clear description of how a DSSI can be used to create a loosely-couple multi-processor
