Short for single inline memory module, SIMM is a memory module developed by Wang laboratories in 1983. The SIMM circuit board that holds six to nine memory chips per board, the ninth chip usually an error checking chip (parity or non parity). The SIMM was used with computers using a 486, early Intel Pentium, and compatible processors. However, because the Pentium is 64-bit and a SIMM is only 32-bits wide, they must be installed two at a time to work properly.
Below is a graphic illustration of a 4 MB SIMM and a diagram pointing out the important features of a SIMM. The SIMM was replaced by DIMMs.