VAX-VMS MSCP Notes:

(MSCP = Mass Storage Control Protocol)

Basic MSCP Storage Examples

+--------------+
| uVAX-3500    |
| CPU          |
| Internal Bus |
+--------------+
| Q-Bus        |    MSCP     +--------------------------+
| KDA-50 ------x-------------x Up to 8 RA Series Drives |
+--------------+    Cables   +--------------------------+
 
 
+--------------+
| VAX-6420     |
| CPU          |
| XMI Bus      |
+--------------+
| BI Bus       |    MSCP     +--------------------------+
| KDB-50 ------x-------------x Up to 8 RA Series Drives |
+--------------+    Cables   +--------------------------+
 
Notes:
1. Each drive requires a cable running back to the adapter
2. Drives numbers are assigned by inserting a numbered (keyed) plug
 

HSC Based MSCP Storage Example

                      +- Another Processor or HSC Could Connect Here
+----------+          |          +--------+
| VAX-6420 |          |          | HSC    |
| CPU      |          |          +--------+
| XMI Bus  |          |          | Unibus | MSCP   +--------------------------+
| CIXCD    |  CI   +--x--+  CI   | UDA-50 x--------x Up to 8 RA Series Drives |
| CI#0-----x-------x SC8 x-------x        | Cables +--------------------------+
+----------+  Bus  +--x--+  Bus  | ?????? |
| BI Bus   |          |          |        | MSCP   +--------------------------+
+----------+          |          | UDA-50 x--------x Up to 8 RA Series Drives |
                      |          |        | Cables +--------------------------+
                      |          +--------+
                      +- Another Processor or HSC Could Connect Here
 
Notes:
1. The HSC (Hierarchical Storage Controller) is a specialized computer that
   manages storage devices
2. The HSC can reorder up to many thousands of drive commands from the CPUs in
   an attempt to improve system performance (elevator algorithms etc.)
3. When the first HSC was introduced, it was actually a PDP-11/73 processor
   running a special version of RSX11. Later versions used different, processors,
   buses, and adapters.

Documentation Links


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Neil Rieck
Kitchener - Waterloo - Cambridge, Ontario, Canada.