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SIMM is an acronym for Singe Inline Memory Module. A SIMM is a circuit board containing memory chips (DRAMs) which plug into a computer's motherboard. The most common SIMMs are 30Pin and 72Pin.

  • Note: 30Pin SIMMs are typically 8-bit (non-parity) or 9-bit (parity).
  • Note: 72Pin SIMMs are typically 32-bit (non-parity) or 36-bit (parity).

30Pin SIMMs or 72Pin SIMMs must be determined. 486 based systems normally .need four 30Pin SIMMs for the same capacity, while you only need a single 72Pin SIMM. Pentium based systems require upgrades of two 72Pin SIMMs at a time.

  • Note: It is important to read the system board manual to verify the upgrade path.

DIMM is an acronym for Dual Inline Memory Module. Now that 64-bit processors are becoming the standard, system designers are moving from using two 72Pin SIMMs to a single 168Pin DIMM.

  • Note: Please refer to DIMM OVERVIEW for further explanation.


1. Composite SIMMs/DIMMs are double sided. This does not always apply.
2. Composite SIMMs/DIMMs use 4Mbit DRAM. This does not always apply.
3. Composite DIMMs/DIMMs are double-bank. This always applies.

1 . Non-Composite SIMMs/DIMMs are double sided. This does not always apply.
2. Non-Composite SIMMs/DIMMs use 16Mbit DRAM. This does not always apply.
3. Non-Composite SIMMs/DIMMs are single-bank. This always applies.


Non-Parity memory is the most commonly used module in the market today. It gives the complete function of parity memory, but at a lower cost. 85% of all systems shipped in the world today use non-parity memory. Non-Parity has nothing to do with the type of DRAM used.

Parity memo was used more often in the past due to the unreliability of DRAMs being shipped. It offered no functionality to the system, but to inform you of a possible error with data transfer in memory. With better reliability with DRAM production and cost conscious customers, parity has almost been eliminated altogether.

  • Note: Some systems are still using parity to generate ECC off of the system board.
  • Note: Some vendors ship parity generation that is a substitute for real parity. Parity generation will work in most cases except when trying to generate ECC or upgrading some UNIX and Novell based operating systems.
  • Note: Some vendors ship Quad-Cas parity that is true parity but is not 100% compatible. This was designed to use fewer chips and reduce cost.

ECC (Error Code & Correct) is used to correct single bit errors that can occur during memory addressing. This is becoming more main stream, as systems require larger amounts of memory and operation systems become memory intensive.

  • Note: Intel is planning to put this function into the future generation of processors to better handle memory. Currently it is a function of the system chip-set.

Ns (Nanosecond)

The speed in which the module reads and writes is measured in nanoseconds. naturally the lower the number the faster the module performs these functions. In most cases, you can mix faster memory (60ns) banks with slower memory banks (70ns), but the faster modules will only be as fast as the slowest memory bank.

30 Pin SIMM (2/3 Chip Design)
1 or 3MB, Non-Parity or Parity

72 Pin SIMM (8 or 12 chip)
4 or 16MB Non-Parity or Parity

72 Pin SIMM (8 or 12 Chip Design)
4 or 16MB Non-Parity or Parity

72 Pin SODIMM (2 or 4 chip)
4 or 8MB Non-Parity 3.3volt or 5 Volt

144 Pin SODIMM (4 or 8 chip)
8 or 16MB Non-Parity 3.3Volt or 5Volt

168 Pin DIMM (4 or 8 chip)
8 or 16MB, Non-Parity, 5 Volt Buffered

168 Pin DIMM (16 or 18 Chip)
32MB Non-Parity or ECC, 5Volt or 3.3Volt, Non-Buffered

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