MS750 Memory System

/750 backplane from behind, showing the slots occupied by the MS750 in the centre

The MS750 Memory System is the main memory for the VAX-11/750; it consists of:

• one Memory Controller module (MCM)
• one to eight memory array modules

The Memory Controller Module connects to the /750's CPU/Memory Interconnect bus, and also to an internal memory bus - which does not seem to have a formal name - which runs to the memory array modules' slots.

The Memory Controller Module (either L0011, L0016, or L0022) resides in a custom slot in the main backplane; slot 10. The memory array modules have their own slots in a dedicated section of the backplane, 8 slots in total. (The physical backplane itself, DEC part number 50-13821/70-16486, is shared with the CPU).

A later version, the MS750-HB which used the then-new L0022 Memory Controller Module, allowed the use of up to two M7199 4MB memory array modules; the older Memory Controller Modules were restricted to smaller memory array modules.

MS750 Memory Controllers

256KB module

There were three different Memory Controller Modules for the MS750:

• L0011 - up to eight M8728 256KB memory array modules = 2MB max.
• L0016 - up to eight M8750 1MB memory array modules = 8MB max.
• L0022 - up to two M7199 4MB memory array modules and six M8750 1MB memory array modules = 14MB max.

(14MB of Memory is the architectural limit of the VAX-11/750)

1MB module

The earlier array modules are also used with the MK11 memory system of the PDP-11/70.

Further reading

• MS750-HB User Guide (EK-MS75H-UG-001) - not online (yet; coming soon, we hope)
• MS750-HB Field Maintenance Print Set (MP-02061) - not online

External links

• VAX-11/750 Memory System Technical Description (EK-MS750-TD-001)
• VAX-11/750 Installation Manual (EK-SI75F-IN-001) - the MS750 is covered in Chapter 9 (pp. 131-132 of the PDF)
• Comet Memory Unit Field Maintenance Print Set (MP01404) - covers the L0016
• M8750 Field Maintenance Print Set (MP01398) - very faint scans
• 11/730-Z Field Maintenance Print Set (MP01270) - the M8750 is covered in MS730-C Field Maintenance Print Set (MP01366) (pp. 292-12 of the PDF)
• L0016 (MCM) - Memory Control image