SIMM

A SIMM, or Single Inline Memory Module, is a type of computer memory module used to add memory to many personal computers and workstations from the late 1980s through the mid-1990s. The name reflects its electrical design: the same data and address lines are presented on both sides of the module, unlike later DIMMs where the lines are separate.

Two common physical forms appeared over its lifespan. The 30-pin SIMM was used in earlier 8- and 16-bit systems, while the more widely adopted 72-pin SIMM supported 32-bit data paths typical of mid- to late-1990s PCs. Modules came with optional parity or ECC to detect or correct memory errors. Capacities varied, but individual SIMMs typically ranged from tens of megabytes to a few hundred megabytes, with higher densities available as technology advanced.

A SIMM is installed in a socket on the motherboard, and memory capacity is often added in matched groups to meet the system’s data-path width and bank requirements. Proper installation and compatibility depended on the motherboard’s supported bus width, parity/ECC options, and the CPU/memory controller. As memory demands grew and bus architectures evolved, SIMMs were gradually superseded by DIMMs, which provide more robust data paths, easier scalability, and longer compatibility with newer memory technologies.

Today, SIMMs are largely obsolete in modern consumer computers, surviving mainly in historical contexts or in legacy systems that still require older hardware. See also memory technologies such as DIMMs, RAM, parity and ECC memory.