Read/Write Memory Modules
Overview
Most memory modules used in the Q-bus platform were dynamic memory, which has a much higher density, is cheaper, but must be constantly refreshed in order to keep it from losing its contents. The MSV11-B is the only dynamic memory module without self refresh, which means it requires a processor with refresh capability, or some other module to provide the refresh function.
DEC made one 8 KB (4 KW) core memory module for the PDP-11/03, the MMV11-A. This was non-volatile memory, in which the contents would survive a power failure. It consumed a lot of power, however, and required two full backplane slots. DEC also made the MCV11 static RAM module, with built-in battery backup, which made it non-volatile, as well. This replaced the MMV11-A, when it was discontinued.
16-Bit and Low Density 18-Bit Memory
The table below contains a breakdown and comparison of early low density memory modules. These are difficult to find and not terribly desirable to own, other than for historical preservation purposes. None of the modules support parity or block mode transfers.
| Module Number | G653+H223 | M7944 | M7955-YA | M7955-YB | M7955-YC | M7955-YD |
|---|---|---|---|---|---|---|
| Model Number | MMV11-A | MSV11-B | MSV11-CA | MSV11-CB | MSV11-CC | MSV11-CD |
| Introduced | 1975 | 1975 | 1976 | 1976 | 1976 | 1976 |
| Discontinued | 1980 | 1980 | ||||
| Module Size | Two Quads | Dual | Quad | Quad | Quad | Quad |
| Q-bus Addressing | 16-bits | 16-bits | 18-bits | 18-bits | 18-bits | 18-bits |
| Data Width | 16-bits | 16-bits | 16-bits | 16-bits | 16-bits | 16-bits |
| RAM Type | core | dynamic | dynamic | dynamic | dynamic | dynamic |
| RAM Amount | 8 KB | 8 KB | 8 KB | 16 KB | 24 KB | 32 KB |
| Technology | Core | MOS | MOS | MOS | MOS | MOS |
| RAM Chip Size | N/A | 4 Kb | 4 Kb | 4 Kb | 4 Kb | 4 Kb |
| Access Time1 | 475 ns | 550 ns | 350 ns | 350 ns | 350 ns | 350 ns |
| Self Refresh | N/A | no | yes | yes | yes | yes |
| Battery Backup | N/A | no | yes | yes | yes | yes |
| AC Bus Load | 1.9 | 1.9 | 2.3 | 2.3 | 2.3 | 2.3 |
| DC Bus Load | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 |
| +5V Load | 7.0 A2 | 0.6 A | 1.1 A | 1.1 A | 1.1 A | 1.1 A |
| +5V BBU Load | N/A | N/A | 0.8 A | 0.8 A | 0.8 A | 0.8 A |
| +5V Total | 7.0 A2 | 0.6 A | 1.9 A | 1.9 A | 1.9 A | 1.9 A |
| +12V Load | 0.60 A2 | 0.30 A | 0.54 A | 0.54 A | 0.54 A | 0.54 A |
| +12V BBU Load | N/A | N/A | 0.16 A | 0.16 A | 0.16 A | 0.16 A |
| +12V Total | 0.60 A2 | 0.30 A | 0.70 A | 0.70 A | 0.70 A | 0.70 A |
1
Maximum performing a DATI operation.
2
While Operational.
18-Bit Memory
DEC only made one 18-bit memory module - the MSV11-D/E, which came in four different sizes, with and without parity. The table below compares these modules.
| Module Number | M8044-AA | M8044-BA | M8044-CA | M8044-DA | M8045-AA | M8045-BA | M8045-CA | M8045-DA |
|---|---|---|---|---|---|---|---|---|
| Model Number | MSV11-DA | MSV11-DB | MSV11-DC | MSV11-DD | MSV11-EA | MSV11-EB | MSV11-EC | MSV11-ED |
| Introduced | 1977 | 1977 | 1977 | 1977 | 1977 | 1977 | 1977 | 1977 |
| Discontinued | ||||||||
| Module Size | Dual | Dual | Dual | Dual | Dual | Dual | Dual | Dual |
| Q-bus Addressing | 18-bits | 18-bits | 18-bits | 18-bits | 18-bits | 18-bits | 18-bits | 18-bits |
| Data Width | 16-bits | 16-bits | 16-bits | 16-bits | 18-bits | 18-bits | 18-bits | 18-bits |
| RAM Type | dynamic | dynamic | dynamic | dynamic | dynamic | dynamic | dynamic | dynamic |
| RAM Amount | 8 KB | 16 KB | 32 KB | 64 KB | 8 KB | 16 KB | 32 KB | 64 KB |
| Technology | MOS | MOS | MOS | MOS | MOS | MOS | MOS | MOS |
| RAM Chip Size | 4 Kb | 4 Kb | 16 Kb | 16 Kb | 4 Kb | 4 Kb | 16 Kb | 16 Kb |
| Access Time3 | 225 ns | 225 ns | 225 ns | 225 ns | 265 ns | 265 ns | 265 ns | 265 ns |
| Self Refresh | yes | yes | yes | yes | yes | yes | yes | yes |
| Parity | no | no | no | no | yes | yes | yes | yes |
| Parity CSR | N/A | N/A | N/A | N/A | no | no | no | no |
| Battery Backup | yes | yes | yes | yes | yes | yes | yes | yes |
| AC Bus Load | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 2 |
| DC Bus Load | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
| +5V Load | 1.7 A | 1.7 A | 1.7 A | 1.7 A | 2.0 A | 2.0 A | 2.0 A | 2.0 A |
| +5V BBU Load | 0.7 A | 0.7 A | 0.7 A | 0.7 A | 1.0 A | 1.0 A | 1.0 A | 1.0 A |
| +5V Total | 2.4 A | 2.4 A | 2.4 A | 2.4 A | 3.0 A | 3.0 A | 3.0 A | 3.0 A |
| +12V Load | 0.34 A | 0.37 A | 0.34 A | 0.37 A | 0.38 A | 0.38 A | 0.41 A | 0.41 A |
3
Maximum performing a DATI operation.
DEC used the M8045 circuit board for the M8044 and left the parity memory bit and parity logic locations unpopulated. As a result, people who are unfamiliar with the differences, will sometimes confuse an M8044 with an M8045.
The module below was represented as an M8045, 18-bit, 32KW memory module. Notice how the parity memory locations from each of the four rows of memory is missing (circled in red), along with the parity generating logic (circled in blue.) The circuit board is clearly etched with the M8045 identification information, however. The second photo does not show the “18 BIT” etched on the board before “MOS MEM”. The ejector handles on this board should be marked with M8044-DA.
22-Bit Memory
The table below compares 22-bit memory modules. These came in various widths and densities.
| Module Number | M8059-FA | M8059-KA | M7506-AA | M7506-BA | M7558-AA | M8067-FA | M8067-KA | M8067-LA | M7551-AA | M7551-BA | M7551-CA |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Model Number | MSV11-LF | MSV11-LK | MSV11-MA | MSV11-MB | MSV11-SA | MSV11-PF | MSV11-PK | MSV11-PL | MSV11-QA | MSV11-QB | MSV11-QC |
| Introduced | 1981 | 1981 | 1986 | 1981 | 1981 | 1981 | 1985 | 1985 | 1985 | ||
| Discontinued | 1982 | ||||||||||
| Module Size | Dual | Dual | Dual | Dual | Dual | Quad | Quad | Quad | Quad | Quad | Quad |
| Q-bus Addressing | 22-bits | 22-bits | 22-bits | 22-bits | 22-bits | 22-bits | 22-bits | 22-bits | 22-bits | 22-bits | 22-bits |
| Data Width | 18-bits | 18-bits | 18-bits | 18-bits | 18-bits | 18-bits | 18-bits | 18-bits | 18-bits | 18-bits | 18-bits |
| RAM Type | dynamic | dynamic | dynamic | dynamic | dynamic | dynamic | dynamic | dynamic | dynamic | dynamic | dynamic |
| RAM Amount | 128 KB | 256 KB | 512 KB | 1 MB | 2 MB | 128 KB | 256 KB | 512 KB | 1 MB | 2 MB | 4 MB |
| Technology | MOS | MOS | MOS | MOS | MOS | MOS | MOS | MOS | MOS | MOS | MOS |
| RAM Chip Size | 64 Kb | 64 Kb | 256 Kb | 256 Kb | 256 Kb | 16 Kb | 64 Kb | 64 Kb | 64 Kb | 256 Kb | 256 Kb |
| Access Time4 | 230 ns | 230 ns | 260 ns | 260 ns | 260 ns | 358 ns | 358 ns | 358 ns | |||
| Self Refresh | yes | yes | yes | yes | yes | yes | yes | yes | yes | yes | yes |
| Parity | yes | yes | yes | yes | yes | yes | yes | yes | yes | yes | yes |
| Parity CSR | yes | yes | yes | yes | yes | yes | yes | yes | yes | yes | yes |
| Block Mode | no | no | yes | yes | yes | yes | yes | yes | yes | yes | yes |
| Battery Backup | yes | yes | yes | yes | yes | yes | yes | yes | yes | yes | yes |
| AC Bus Load | 2 | 2 | 2 | 2 | 2 | 2 | 2 | 1.9-2.4 | |||
| DC Bus Load | 0.5 | 0.5 | 1 | 1 | 1 | 1 | 1 | 0.5 | |||
| +5V Load | 1.45 A | 1.60 A | 1.45 A | 1.70 A | 1.70 A | 1.0 A | 1.0 A | 1.0 A | |||
| +5V BBU Load | 0.90 A | 1.00 A | 1.20 A | 1.75 A | 1.85 A | 1.4 A | 1.3 A | 1.5 A | |||
| +5V Total | 2.35 A | 2.60 A | 2.19 A | 2.22 A | 2.65 A | 3.45 A | 3.60 A | 2.4 A | 2.3 A | 2.5 A | |
| +12V Load | N/A | N/A | N/A | N/A | 0.35 A | N/A | N/A | N/A | N/A | N/A |
4
Maximum performing a DATI operation.
PMI Memory
The table below compares 22-bit memory modules, with Error Checking and Correction (ECC) and Private Memory Interconnect (PMI) capability. These modules require a Q22/CD backplane slot in either an H9276 or H9276-A backplane, and will be damaged if installed in a Q/Q slot. They also require an M8190 or M8981 processor module, in order to benefit from the PMI feature. They will function as a standard memory module with any other processor, however.
| Module Number | M8637-DA | M8637-EA |
|---|---|---|
| Model Number | MSV11-JD | MSV11-JE |
| Introduced | 1985 | 1985 |
| Discontinued | ||
| Module Size | Quad | Quad |
| Q-bus Addressing | 22-bits | 22-bits |
| Data Width | 18-bits | 18-bits |
| RAM Type | dynamic | dynamic |
| RAM Amount | 1 MB | 2 MB |
| Technology | MOS | MOS |
| RAM Chip Size | 256 Kb | 256 Kb |
| PMI Support | yes | yes |
| Self Refresh | yes | yes |
| Parity | ECC | ECC |
| Parity CSR | yes | yes |
| Block Mode | yes | yes |
| Battery Backup | yes | yes |
| AC Bus Load | 2.5 | 2.5 |
| DC Bus Load | 0.5 | 0.5 |
| +5V Load | 0.5 A | 0.5 A |
| +5V BBU Load | 1.0 A | 1.2 A |
| +5V Load w/BBU | 1.5 A | 1.7 A |
| +12V Load | N/A | N/A |
It is important to note that there are two other variants of the M8637, which are the M8637-BA and M8637-CA. These two modules will only work in a UNIBUS machine, such as a PDP-11/84.
Other Modules with Memory
The following are other DEC modules equipped with memory.
| Module Number | M8631-AA | M8631-CA | M8047-AA | M8047-CA | M8047-HA | M7195-FA |
|---|---|---|---|---|---|---|
| Model Number | MCV11-DA | MCV11-DC | MXV11-AA | MXV11-AC | MXV11-HA | MXV11-BF |
| Introduced | 1981 | 1981 | 1980 | 1980 | 1981 | 1983 |
| Discontinued | ||||||
| Module Size | Dual | Dual | Dual | Dual | Dual | Dual |
| Q-bus Addressing | 22-bits | 22-bits | 18-bits | 18-bits | 18-bits | 22-bits |
| Data Width | 16-bits | 16-bits | 16-bits | 16-bits | 18-bits | 16-bits |
| RAM Type | static | static | dynamic | dynamic | dynamic | dynamic |
| RAM Amount | 8 KB | 32 KB | 8 KB | 32 KB | 32 KB | 128 KB |
| Technology | MOS | MOS | MOS | MOS | MOS | MOS |
| RAM Chip Size | 2 Kb | 2 Kb | 4 Kb | 16 Kb | 16 Kb | 64 Kb |
| Self Refresh | N/A | N/A | yes | yes | yes | yes |
| Parity | no | no | no | no | yes | no |
| Parity CSR | N/A | N/A | N/A | N/A | no | N/A |
| Block Mode | no | no | no | no | no | no |
| Battery Backup | yes | yes | no | no | no | yes |
| AC Bus Load | 2 | 2 | 2 | 2.3 | ||
| DC Bus Load | 2 | 2 | 2 | 0.5 | ||
| +5V Load | 1.20 A | 1.23 A | 1.2 A | 1.2 A | 1.2 A | 3.5 A |
| +5V Load w/BBU | 1.30 | 1.33 | 0.87 A | |||
| +12V Load | N/A | N/A | 0.01 A | 0.01 A | 0.01 A | 0.06 A |
Summary
The memory module needed for a system would depend on availability, the processor being used and the operating system. For a PDP-11/03 system, an M8044/45, with 64 KB would be perfect, as it would provide the maximum amount of memory the system could handle, for a very low cost.
For an average PDP-11/23, or 73 system, the M7506 dual width modules have good capacity and take up little space. For larger systems running Unix, however, it would be best to go with a 2-4 MB M7551 module.
Non-parity modules should not be used, except for PDP-11/03 systems. This is because some of the more complex operating systems require parity memory support. Modules without block mode DMA support should not be used with block mode DMA devices, such as the RDQX series Winchester controllers.
PMI modules should work with any 18-bit or 22-bit processor, but require a Q22/CD slot. They are intended to be used with the LSI-11/83 and 93 processors, however.
Other manufacturers, such as Camintonn and Dataram, made excellent memory products. Some of these are listed on another page, on this site.
References
- LSI-11, PDP-11/03 User’s Manual, 3rd Edition, May 1976 (EK-LSI11-TM-003)
- LSI-11 Systems Service Manual, 5th Edition, January 1985 (EK-LSIFS-SV-005)
- MSV11-C User’s Manual, 1st Edition, December 1976 (EK-MSV11-OP-001)
- MSV11-D, -E User’s Manual, 1st Edition, December 1977 (EK-MSV1D-OP-001)
- MSV11-J MOS Memory User’s Manual, 1st Edition, May 1985 (EK-MSV1J-UG-001)
- MSV11-L User’s Manual, 1st Edition (EK-MSV0L-UG-001)
- MSV11-M User’s Manual, 1st Edition (EK-MSV1M-UG-001)
- MSV11-P User Guide, 1st Edition, August 1981 (EK-MSV0P-UG-001)
- MSV11-Q User’s Guide, 2nd Edition, May 1985 (EK-MSV1Q-UG-002)
- Memories and Peripherals Handbook, 1978-1979 (EB-15114-78)
- Microcomputer Products Handbook, 1985 (EB-26078-41)
Additional Resources
- MicroNote 5 - Q22 Compatible Options
- MicroNote 12 - DMA on the Q-bus
- MicroNote 28 - MSV11-Q/M/J Memory Comparisons
- MicroNote 30 - Private Memory Management Between the KDJ11-B and the MSV11-J
- MicroNote 31 - MSV11-QA Revision Differences
