SIMM -- The Single In line Memory Module is a PC memory module introduced around 1990. The SIMM consists of a small circuit board with memory chips mounted on it. There are two standard formats -- 30 and 72 pin as well as a number of proprietary formats used by individual vendors. The number of pins refers to the number on one side of the SIMM. Double sided SIMMs exist and have 72 active pins on each side. The terms single and double sided refer to whether the pins on both sides are active, not to whether components are mounted on one or two sides. 1, 4, and 16mb SIMMs are generally single sided. 2, 8 and 32mb SIMMs are usually double sided. Single vs double sided seems to be largely a function of the pinout of the memory chips used and whether it is easy mechanically to wire the SIMM circuit board such that the two sets of input and output pins do not conflict. Some motherboards do not wire the second side of some or all SIMM sockets and will only use half of a double sided SIMM. These will generally work satisfactorily, but only half the memory on the SIMM will be available.

For pinouts refer to web site,

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