Source : Free On-Line Dictionary of Computing

Dual In-line Memory Module
     
         Small circuit boards carrying memory {integrated
        circuits}, with signal and power pins on both sides of the
        board, in contrast to {single-in-line memory modules} (SIMM).
     
        The individual gold or lead connectors (pins) on SIMMs,
        although they are on both sides of the chip, are connected to
        the same memory chip, while on a DIMM, the connections on each
        side of the module connect to different chips.  This allows
        for a wider data path, as more modules can be accessed at
        once.  DIMM pins are arranged in a zigzag design to allow PCB
        tracks to pass between them.
     
        The 8-byte DIMM format with dual-sided contacts can
        accommodate 4- and 16-megabit {dynamic RAM} chips, and is
        predicted to handle 64- and 256-Mbit devices.  The 8-byte DIMM
        will hold up to 32 megabytes of memory using 16-Mbit DRAMs,
        but with the 256-Mbit future-generation DRAM, it will be able
        to hold a 64-Mx64 configuration.  Another variation, the
        72-pin {SO-DIMM}, is designed to connect directly to 32 bit
        data buses, and is intended for use in memory-expansion
        applications in {notebook computers}.
     
        A Dual in-line memory module (DIMM), as opposed to SIMMs (used
        by the majority of the PC industry) allows for a 128-bit data
        path by interleaving memory on alternating memory access
        cycles.  SIMMs on the other hand, have a 64-bit data path.
        Suppliers are unanimous in their belief that the DIMM will
        eventually replace the SIMM as the market's preferred memory
        module.
     
        (1996-01-28)