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.