SIMM

SIMMs were invented in 1983 by James E. Clayton[2] at Wang Laboratories with subsequent patents granted in 1987.

Non-IBM PC computers such as UNIX workstations may use proprietary non-standard SIMMs.

The rule of thumb is a 286, 386SX, 68000 or low-end 68020 / 68030 (e.g. Atari Falcon, Mac LC) system (using a 16 bit wide data bus) would require two 30-pin SIMMs for a memory bank.

However, some Pentium systems have support for a "half bank mode", in which the data bus would be shortened to only 32 bits to allow operation of a single SIMM.

Conversely, some 386 and 486 systems use what is known as "memory interleaving", which requires twice as many SIMMs and effectively doubles the bandwidth.

These were soon replaced by ZIF sockets in which the SIMM was inserted at an angle, then tilted into an upright position.

To remove one, the two metal or plastic clips at each end must be pulled to the side, then the SIMM must be tilted back and pulled out (low-profile sockets reversed this convention somewhat, like SODIMMs - the modules are inserted at a "high" angle, then pushed down to become more flush with the motherboard).

Several CPU cards from Great Valley Products for the Commodore Amiga used special 64-pin SIMMs (32 bits wide, 1, 4 or 16 MB, 60 ns).

Dual-ported 64-pin SIMMs were used in Apple Macintosh IIfx computers to allow overlapping read/write cycles (1, 4, 8, 16 MB, 80 ns).