Memory-Presence Determination
SIMMs/DIMMs 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 / DIMM 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, 60ns).
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. 60ns and Reduced CAS-timing (-2ns) appr. CAS = 19ns)
XMx32 is Non parity and XMx36 is Parity .
DIMM Identification (Dual Inline Memory Module)
168-pin memory DIMMs can be usually identified by the information on the chip modules.
(e.g. 2Mx64, 60 ns, EDO). To determine the DIMM capacity from this example, divide
64-bits by 8 (1-byte) and multiply this result by 2M, hence, DIMM = 16MB
XMx32 is Non parity and XMx36 is Parity .
Please see the LEGAL - Trademark notice.
PC100 DIMM Identification (100MHz Dual Inline Memory Module)
Assembled DIMM Naming Convention (Intel)
In order to be able to visually identify the critical parameters of a given DIMM, the following naming convention will
be used.
On component or sticker on DIMM:
PCX-abc-def R
X
= MHz (X=100 for PC100-DIMM)
a
= CL value (CAS latency / cycles (must be <= 3))
b
= trcd value (RAS-to-CAS delay / cycles)
c
= trp value (RAS precharge time / cycles)
d
= tac value (data output valid after / ns)
e
= spd rev# (SPD-EEPROM-version / 2 = rev. 1.2 (or 012))
f
= reserved (always 0)
R
= registered (R = buffered DIMM or w/o -R- for unbuffered DIMM)
Example - 1: PC100-322-620
100MHz, CAS latency = 3 cycles, RAS-CAS delay = 2 cycles, RAS precharge = 2 cycles,
data out valid after 6 ns, revision 1.2, unbuffered DIMM.
Example - 2: PC100-322-60120
100MHz, CAS latency = 3 cycles, RAS-CAS delay = 2 cycles, RAS precharge = 2 cycles,
data out valid after 6 ns, revision 1.2, unbuffered DIMM.
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 trough 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 0Measure
-mentSingle 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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