A single inline memory module (SIMM) consists of a number of memory components (usually black) that are attached to a printed circuit board (usually green). The gold or tin pins on the bottom of the SIMM provide a connection between the module and a socket on a larger printed circuit board. The pins on the front and back of a SIMM are connected, providing a single line of communication paths between the module and the system.
72-pin SIMMs are commonly found in older desktop computers, such as the 486 and early Pentium models. Each 72-pin SIMM provides a 32-bit data path, so they can be installed singly in 32-bit systems (486 models) but must be installed in pairs in 64-bit systems (Pentium and Athlon models). 72-pin SIMMs are available in FPM or EDO. When upgrading, be sure to match the memory technology that is already in your system.