Difference between revisions of "Digital Storage Systems Interconnect"

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(More detail about DSSI; should move SCA stuff to SCA article, and include "CI PPD Architectural Layers" diagram instead)
(Substitute diagram showing the relationship between the DSSI and the CI's physical layer, for the SCA diagram)
Line 3: Line 3:
 
DSSI is a 8-bit wide [[parallel]] bus. It is an alternate physical layer in the [[Computer Interconnect]] system; the CI system had a 'native' physical layer before the creation of DSSI. The DSSI specification lists the main attributes of DSSI as: multi-drop linear bus electrical topology; 8-bit parallel; low-cost, [[single-ended signalling]] interface circuitry; [[direct current|DC]] coupling.
 
DSSI is a 8-bit wide [[parallel]] bus. It is an alternate physical layer in the [[Computer Interconnect]] system; the CI system had a 'native' physical layer before the creation of DSSI. The DSSI specification lists the main attributes of DSSI as: multi-drop linear bus electrical topology; 8-bit parallel; low-cost, [[single-ended signalling]] interface circuitry; [[direct current|DC]] coupling.
  
Description from the 'Digital's Storage System Interconnect' protocol specification document:
+
The relationship between the DSSI and the CI's physical layer is shown in the following diagram:
 +
<pre>
 +
                                                          <-----+
 +
                        +---------------------+                |
 +
                        | Port Driver        |                |
 +
                        | Layer              |                |
 +
                        | ( SCA Specification)|                |
 +
                        +---------------------+                |
 +
                                  |                            |
 +
                                  |                            |
 +
                        .......................                |
 +
                        . CI Port Adapter    .                |
 +
                        . ( eg: VAX CI Port ) .                |
 +
                        .......................                |
 +
                                  |                            | P
 +
      +------>                    |                            | P
 +
      |                +---------------------+                | D
 +
      |                |    CI Port        |                |
 +
    C |                |    Layer          |                | L
 +
    I |                |  ( DEC Std 161 )  |                | A
 +
      |                +---------------------+                | Y
 +
    A |                    |              |                    | E
 +
    R |            +------+              +------+            | R
 +
    C |            |                            |            |
 +
    H |  +----------------------+      +---------------------+  |
 +
    I |  | DSSI Datalink        |      |    CI Datalink      |  |
 +
    T |  |    Layer            | .... |      Layer          |  |
 +
    E |  | ( DSSI Spec. )      |      |  ( Dec Std 161 )    |  |
 +
    C |  +----------------------+      +---------------------+  |
 +
    T |            |                            |      <-----+
 +
    U |            |                            |      <-----+ P L
 +
    R |  +----------------------+      +---------------------+  | H A
 +
    E |  |    DSSI Physical    |      |    CI Physical      |  | Y Y
 +
      |  |    Interconnect      |      |    Interconnect     |  | S E
 +
      |  |    ( DSSI Spec. )    |      |  ( DEC Std 161 )  |  | I R
 +
      |  +----------------------+      +---------------------+  | C
 +
      +------>                                            <-----+ A
 +
                                                                  L
  
[[File:The SCA Model.png|thumb|right|350px|Systems Communication Architecture]]
+
                Figure 1-2:  CI PPD Architectural Layers
 +
</pre>
 +
 
 +
A description of the DSSI 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 .. that combine a common host interface and port layer with an implementation-specific datalink and physical interconnect.
 
  "The DSSI, supporting the needs of low-end and mid-range systems, is one in a family of high-performance computer-to-computer interconnects .. 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]."
+
  CI-class interconnects provide the transmission services required by Digital's [[System Communication Architecture]] (SCA) - a four-tiered set of protocols and interfaces.."
  
DSSI made it possible to build [[VAXcluster]]s from [[MicroVAX]] and smaller [[VAX]] computers by adding CI-bus functionality to smaller VAX systems.
+
DSSI thus made it possible to build [[VAXcluster]]s from [[MicroVAX]] and smaller [[VAX]] computers by adding CI-bus functionality to smaller VAX systems.
  
== Family of DSSI Products==
+
== DSSI Controllers/Interfaces ==
 
 
=== DSSI Controllers/Interfaces ===
 
  
 
* [[KFQSA]] [[QBUS]] DSSI Adapter
 
* [[KFQSA]] [[QBUS]] DSSI Adapter
Line 27: Line 65:
 
* [[KFA40]] [[DEC 4000]] I/O Module
 
* [[KFA40]] [[DEC 4000]] I/O Module
  
=== DSSI [[Hierarchical Storage Controller]]s (HSDs) ===
+
== DSSI Hierarchical Storage Controllers (HSDs) ==
 +
 
 +
[[Hierarchical Storage Controller]]s:
  
 
* [[HSD05]]
 
* [[HSD05]]
Line 34: Line 74:
 
* [[HSD50]]
 
* [[HSD50]]
  
=== DSSI Disk Drives ===
+
== DSSI Disk Drives ==
  
 
* [[RF30]]
 
* [[RF30]]
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* [[RF75]]
 
* [[RF75]]
  
=== DSSI Tape Drives ===
+
== DSSI Tape Drives ==
  
 
* [[TF30]]
 
* [[TF30]]

Revision as of 02:55, 1 September 2023

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 is a 8-bit wide parallel bus. It is an alternate physical layer in the Computer Interconnect system; the CI system had a 'native' physical layer before the creation of DSSI. The DSSI specification lists the main attributes of DSSI as: multi-drop linear bus electrical topology; 8-bit parallel; low-cost, single-ended signalling interface circuitry; DC coupling.

The relationship between the DSSI and the CI's physical layer is shown in the following diagram:

                                                          <-----+
                        +---------------------+                 |
                        | Port Driver         |                 |
                        | Layer               |                 |
                        | ( SCA Specification)|                 |
                        +---------------------+                 |
                                  |                             |
                                  |                             |
                        .......................                 |
                        . CI Port Adapter     .                 |
                        . ( eg: VAX CI Port ) .                 |
                        .......................                 |
                                  |                             | P
      +------>                    |                             | P
      |                 +---------------------+                 | D
      |                 |     CI Port         |                 |
    C |                 |     Layer           |                 | L
    I |                 |   ( DEC Std 161 )   |                 | A
      |                 +---------------------+                 | Y
    A |                    |               |                    | E
    R |             +------+               +------+             | R
    C |             |                             |             |
    H |  +----------------------+      +---------------------+  |
    I |  | DSSI Datalink        |      |    CI Datalink      |  |
    T |  |    Layer             | .... |      Layer          |  |
    E |  | ( DSSI Spec. )       |      |  ( Dec Std 161 )    |  |
    C |  +----------------------+      +---------------------+  |
    T |             |                             |       <-----+
    U |             |                             |       <-----+ P L
    R |  +----------------------+      +---------------------+  | H A
    E |  |    DSSI Physical     |      |    CI Physical      |  | Y Y
      |  |    Interconnect      |      |    Interconnect     |  | S E
      |  |    ( DSSI Spec. )    |      |   ( DEC Std 161 )   |  | I R
      |  +----------------------+      +---------------------+  | C
      +------>                                            <-----+ A
                                                                  L

                Figure 1-2:  CI PPD Architectural Layers

A description of the DSSI 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 .. 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 System Communication Architecture (SCA) - a four-tiered set of protocols and interfaces.."

DSSI thus made it possible to build VAXclusters from MicroVAX and smaller VAX computers by adding CI-bus functionality to smaller VAX systems.

DSSI Controllers/Interfaces

DSSI Hierarchical Storage Controllers (HSDs)

Hierarchical Storage Controllers:

DSSI Disk Drives

DSSI Tape Drives

External Links