SIMM (Single in-line memory module) - the name of memory modules with a single row of contacts, widely used in computer systems in the 1990s. SIMM standards are described in JEDEC JESD-21C. They had several modifications.
Most early IBM PC-compatible computer motherboards used DRAM chips packaged in DIP cases and mounted in sockets. However, systems with 80286 processors used more memory, and to save motherboard space and simplify the upgrade process, individual chips were combined into modules. Some systems used SIPP modules, but they proved too easy to break during installation.
SIMM modules were developed and patented in 1983 by Wang Laboratories. Originally the modules were ceramic and had pins.
Early SIMMs were installed in slots that had no locking mechanisms, but fairly quickly ZIF slots with latches became common.
The first to appear were 30-pin modules with a capacity of 64kbytes to 16Mbytes and an eight-bit data bus, supplemented (sometimes) by a ninth memory parity line. They were used in computers with Intel 8088, 286, 386 CPUs. Modules were used on motherboards with 8088 processors one by one, on 286 and 386SX ones in pairs, on 386DX four modules of equal capacity.
With the spread of mass-produced computers in the Intel 80486 processors and similar, for which 30-pin modules had to be put at least four, 30-pin SIMM modules were superseded by 72-pin SIMM modules. 72-pin modules consisted essentially of four 30-pin modules with common address lines and separate data lines, were 32-bit, had a capacity of 1 Mbyte to 64 Mbytes. In the era of 486 processors, 72-pin modules were used on brand-name PCs (Compaq, HP, Acer and others), and with the transition to Pentium processors - on almost all motherboards from all manufacturers.
Since motherboards for Pentium processors with a 64-bit data bus needed to put 72-pin modules in pairs, gradually the modules were physically paired "together": they began to place the chips on both sides of the printed circuit board memory module. As a result, the first DIMM modules appeared.
There were also 64-pin modules (used, for example, in Macintosh IIfx computers) and 68-pin modules (for example, VRAM in Macintosh LC).
