SIMM

A SIMM, or single in-line memory module, is a type of memory module containing random-access memory used in computers from the early 1980s to the late 1990s. It differs from a dual in-line memory module (DIMM), the most predominant form of memory module today, in that the contacts on a SIMM are redundant on both sides of the module. SIMMs were standardised under the JEDEC JESD-21C standard.

Most early PC motherboards (8088-based PCs, XTs, and early ATs) used socketed DIP chips for DRAM. As computer memory capacities grew, memory modules were used to save motherboard space and ease memory expansion. Instead of plugging in eight or nine single DIP chips, only one additional memory module was needed to increase the memory of the computer.

SIMMs were invented in 1982 by James J. Parker at Zenith Microcircuits and the first Zenith Microcircuits customer was Wang Laboratories. Wang Laboratories tried to patent it and were granted a patent in April 1987. That patent was later voided when Wang Laboratories sued multiple companies for infringement and it was then publicized that they were the prior invention of Parker at Zenith Microcircuits (the Elk Grove Village, Illinois subsidiary of Zenith Electronics Corporation). The lawsuit was then dropped and the patent was vacated. The original memory modules were built upon ceramic substrates with 64K Hitachi "flip chip" parts and had pins, i.e. single in-line package (SIP) packaging. There was an 8-bit part and a 9-bit part both at 64K.The pins were the costliest part of the assembly process and Zenith Microcircuits, in conjunction with Wang and Amp, soon developed an easy insertion, pinless connector. Later the modules were built on ceramic substrates with Fujitsu plastic J-lead chips and still later, they were made on standard PCB material. SIMMs using pins are usually called SIP or SIPP memory modules to distinguish them from the more common modules using edge connectors.

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