PS/2 Memory Reference

PS/2 SIMM Memory SYSTEM-BOARD Matrix

For the memory cross-reference table go HERE.

In the case of the 16MB ECC IBM uses the pins 69 & 67 tied against 72 (GND) to recognize it as 16MB / 70 ns ECC... which is accidentally the same coding as for the 16MB / 70 ns Parity. Unlike to that the ECC SIMM has pin 48 tied to GND as well - the Parity and Non-Parity modules have this pin not connected.

8MB has pin 69 tied to ground.

Usually the 32MB / 70 ns SIMMs use the PD pattern 70 & 67 open, 68 & 69 closed (GND). The ECC / Non-ECC determination is pin 48 on the module, which is open on Non-Parity and Parity and GND on ECC modules. So from the presence-detect part of the story 60 ns modules *could* be reworked.

The problem is the level of integration of the ECC on the module. The "original" IBM ECC modules are 40-bit modules: 32 (4 x 8) data bits, 4 x 1 ECC bits, 4 x 1 spare bits. The ECC logic is part of the system board. There are different ECC structures, which use 36-bit memory (parity) and a particular signaling if the memory integrity is void, there are modules with lesser bits per module (38 or 39) and modules with "ECC On SIMM" (EOS), which have the ECC logic on the module and the planar "thinks" they were Parity modules. There is only a logic signal present that signals a failing module to the planar logic in case a correctable ECC error occurred. (In case of a non-correctable ECC error you land on a memory error anyway).

However I don't (yet) know which coding they use. 32MB Parity and 32MB Non-Parity use 67 & 70 open, 68 & 69 shortened to 72 (GND). Most likely this same pattern applies to the 32MB ECC as well.


OEM-Memory Modules Specification (by Manufacturer)

Type ID, OEM P/2 FRU
Kingston
8 MB ECC KTM1159  
16 MB ECC KTM3720  
32 MB ECC KTM9595  
Viking
8 MB ECC I1159 92G7208
16 MB ECC I3720 92G7209
32 MB ECC I7210 92G7210
4 MB ? I128 92G7200
8 MB ? I130 92G7203
Mcglen Micro (Viking Components)
16 MB ECC DP16I3720  
32 MB ECC DP32I7210   
2 MB ? DP2I902  
4 MB ? DP4I128  
8 MB ? DP8I130  
PNY Has only the Lacuna-76 / -77 in their current list, but the 4/8/16MB modules from the PS/VP-2 should fit in there.
4 MB / 70 ns P P-92G7201  (no longer available)
8 MB / 70 ns P P-92G7204  (no longer available)
16 MB / 70 ns P P-92G7204  IBM 92G7204 / 60G2950
PIICEON
4 MB / 70 ns P 907-0345  IBM 92G7200
8MB/70n P 900-0070  IBM 92G7203
16 MB / 70 ns P 907-0716 under PS/VP IBM 92G7204 / 60G1622
8 MB ECC 907-9508 2 x IBM 6451158 / 4MB
16 MB ECC 907-9516 2 x IBM 6451159 / 8MB
TRANSCEND
2 MB / 70 ns P TS2M0902 IBM 6540902
4 MB / 70 ns P TS4M0128 IBM 6540128 / 92G7200 / 70G9820
8 MB / 70 ns P TS8M0130 IBM 6540130 / 92G7203 / 070PS8Y
16 MB / 70 ns P
8 MB ECC TS8M1159 IBM 6541159
16 MB ECC TS16M3720 IBM 32G3720
32 MB ECC TS32M7210 IBM 92G7210 / 070E32Y

Memory-Presence Determination

SIMMs that are not clearly labeled cannot be identified other than by part number. 

(For MEMORY component define, you will have the need to know about 70 or more timing/temperature parameters. Because this information will not fit on a SIMM normally only P/N / Speed and Size is printed on a small Label). 

SIMM Identification (Single Inline Memory Module)
72-pin memory SIMMs are usually marked with a label that shows the size and speed (e.g. 1Mx32, 60 ns). To determine the SIMM capacity from the above example, divide 32-bits by 8 (1-byte) and multiply this result by 1M, hence, SIMM = 4MB (SIMMs prefix -6R = RAS max. 60 ns and Reduced CAS-timing (-2 ns) appr. CAS = 19 ns)
XMx32 is Non parity and XMx36 is Parity.

PS/2 72-Pin SIMMs (for M/T 85xx/95xx)
A set of 4-bits shows the state of the presence detect signals for a specific memory connector. The setting of the presence-detect bits is determined through registers (x'00E8' and x'00E9'). 

Not all of the following Memory-modules are supported by every IBM computer.

Pin 72 to Pin 70, 69, 68 and 67 ( X = connected to GND)

Presence-Detect Bits Table

Bits.
3 2 1 0
Measure
-ment
Single Inline Memory - Module Definition
1101
..X.
32MB 60-ns Industry standard
1001
.XX.
32MB 70-ns Industry standard
0101
X.X.
32MB 80-ns Industry standard
1110
...X
16MB 60-ns Industry standard
1010
.X.X
16MB 70-ns IBM and Industry standard
0110
X..X
16MB 80-ns Industry standard
1011
.X..
8MB 70-ns IBM and Industry standard
1000
.XXX
8MB 80-ns IBM and Industry standard
1000
.XXX
4MB 70-ns Industry standard
0100
X.XX
4MB 70-ns IBM
0100
X.XX
4MB 80-ns Industry standard
0000
XXXX
4MB 80-ns IBM
1001
.XX.
2MB 70-ns Industry standard
1100
..XX
2MB 70-ns IBM
0101
X.X.
2MB 80-ns Industry standard
1001
.XX.
2MB 80-ns IBM
0101
X.X.
2MB 85-ns IBM
1110
...X
2MB 100-ns IBM
1010
.X.X
1MB 70-ns Industry standard
0110
X..X
1MB 80-ns Industry standard
0110
X..X
1MB 85-ns IBM
0010
XX.X
1MB 100-ns IBM
1111
  Connector is empty

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