A SIMM, also referred to as a RAM stick, is a tiny circuit board that houses memory cells. The Memory setup in a computer can be changed by inserting a SIMM into a port on the processor. The number of memory processors and their individual capacities determine how much RAM is contained in a SIMM.

Prior to the invention of SIMMs, computer memory was inserted into system slots one chip at a time. SIMMs were created to reduce the amount of room needed on the processor and to make it simpler to add bigger amounts of memory at once. Early SIMMs allowed an 8-bit data channel and had 30 interface lines. Subsequent SIMMs used a 32-bit data path to the Processor, raised the number of pins to 72, and added an off-center cut to aid in fitting. SIMMs had to be placed in corresponding pairs in order to function correctly once computers started using a 64-bit interface.

In the end, DIMMs, which allowed a 64-bit data interface, took the position of SIMMs as the default memory module. In contrast to a SIMM, which has similar electrical contact pins on both faces of the module, a DIMM has unique pins on each side. DIMMs could also be used one at a time, instead of needing identical sets.