SIMM is a type of computer memory used in x86 and Pentium family of computers. It consists of a small circuit board with RAM chips and plugs into sockets running an 8- or 32-bit bus. There are two types: a 30-pin module for older x86 computers and a 72-pin module common in 486 and Pentium systems. SIMMs were later replaced by DIMMs. Installing SIMMs is a simple process, but always refer to technical manuals before performing any upgrades.
SIMM, which stands for single inline memory module, is a type of computer memory used in x86 and Pentium family of computers, as well as select laser printers. A SIMM consists of a small circuit board that contains two to more than 32 random access memory (RAM) chips and plugs into sockets running an 8- or 32-bit bus. There are two distinct types: a 30-pin module for older x86 computers and a 72-pin module common in 486 and Pentium systems. Modules can contain parity or no parity.
The first SIMM module was created in 1983 by James Clayton of Wang Laboratories and used exclusively in IBM PS/2 computers. Soon after, SIMMs became the standard for memory modules, replacing socketed DIP and SIPP memory chips that took up much more space on the motherboard. SIMMs were later replaced by the dual in line memory module, or DIMM.
Of the two types of SIMMs, the older 30-pin module ranges in size from 256 kilobytes up to 16 Megabytes (MB). Each module supplies one byte, or 8 bits, plus an additional bit if the parity chip is present, of data. In contrast, the 72-pin module can range in size from 1MB up to 2.048MB and provide four bytes or 32 bits of data at a time. Two notches, one at the end and the other in the center, help guide the SIMM into the correct position on the socket. Single-sided and double-sided configurations are available.
One of the main differences between SIMMs and DIMMs lies in the location of the electrical pins or contacts. The contacts along the leading edge of a SIMM repeat again at the rear. The contacts on DIMMs differ on each side. Data path size is another notable difference between DIMM and SIMM. DIMMs use a 64-bit data path while SIMMs are limited to 32-bit. Finally, SIMMs must be installed in pairs to function properly while only one DIMM is required at a time.
Installing SIMMs as part of a computer memory upgrade is a fairly simple process. Always refer to the technical manuals before performing any upgrades to verify the memory type.
First, shut down and unplug your computer. Remove the case and look for the memory slots on the motherboard. Dissipate extra static electricity by touching a metal object. Then, holding the memory module by its edges to avoid direct contact with the pins, insert the module into an empty socket at a 60° angle and rotate it into place until the module is perpendicular to the motherboard. Replace the computer cover, reconnect the cables, and turn on the computer. In most cases, the system should recognize the new memory.
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