System Memory
The system memory consists of RAM soldered on the system board and
socketed Single In-line Memory Module (SIMM). Machine Types 2133,
2155, and 2168 contain a 386SX, 486SX, 486DX, or 486DX2 system board.
The 386SX system board (72-pin memory SIMM) has either 2MB or 4MB of
RAM soldered on. Two 72-pin sockets are available to add SIMMs. SIMMs
supported are 1MB, 2MB, 4MB, and 8MB. SIMM speed is from 70 ns to 85
ns. Sockets can accept either size and speed. When two SIMMs of the
same size and speed are installed, interleaving can occur. A POST error
code 225, “Unsupported SIMM” appears on the display when an installed
SIMM is the wrong value.
The 486SX and 486DX system boards (30-pin memory SIMMs) have no
soldered RAM. All system memory is socketed with SIMMs. 30-pin SIMMs
are installed in banks of four each. One or both banks must be occupied.
Each bank must contain SIMMs of the same size and speed. Interleaving of
memory occurs on these system boards. SIMMs supported are 80 ns or
faster. Faster speeds are numbers less than 80 ns. SIMMs must be 9 bits
wide. No POST error is displayed when a SIMM of the wrong value is
installed.
The 486SX, 486DX, and 486DX2 system boards (72-pin memory SIMM)
have no soldered RAM. All system memory is socketed with SIMMs. Unlike
30-pin SIMMs, which must be installed in banks of four, 72-pin memory
SIMM can be installed one at a time. SIMMs supported are 70 ns and must
be 36 bits wide.
SIMM Identification
30-Pin Memory SIMMs:
30-pin memory SIMM size and speed can be diffi-
cult to identify. By looking at the numbers on the SIMM chips, you can
attempt to identify the size and speed of the SIMM. The size of the SIMM is
generally imbedded in the chip part number and the speed generally follows
the number.
For example: XXX256XX - 8 (X can be any number or letter) would be a
256K SIMM and have a speed of 80 ns. XXXX1000X - 7 would be a 1MB
SIMM and have a speed of 70 ns. XXXX256X - 15 would be an unsup-
ported SIMM since it has a speed of 150 ns. There are many variations to
this. Consult the SIMM manufacturer documentation to identify SIMM values
when you are unsure of the SIMM value in the system.
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