SIMM

A SIMM, or single in-line memory module, is a type of memory module containing random access memory used in computers from the early 1980s to the late 1990s. It differs from a dual in-line memory module (DIMM), the most predominant form of memory module today, in that the contacts on a SIMM are redundant on both sides of the module. SIMMs were standardised under the JEDEC JESD-21C standard.
Most early PC motherboards (8088-based PCs, XTs, and early ATs) used socketed DIP chips. With the introduction of 286-based IBM XT/286, which could use larger amounts of memory, memory modules evolved to save motherboard space and to ease memory expansion. Instead of plugging in eight or nine single DIP DRAM chips, only one additional memory module was needed to increase the memory of the computer. A few 286-based computers used (often non-standard) memory modules like SIPP memory (single in-line pin package). The SIPP's 30 pins often bent or broke during installation...