A SIMM is a type of memory module used in computers from the early 1980s to the early 2000s. It is a printed circuit board on which has random-access memory attached to one or both sides. It differs from a dual in-line memory module (DIMM), the most predominant form of memory module since the late 1990s, in that the contacts on a SIMM are redundant on both sides of the module. SIMMs were standardised under the JEDEC JESD-21C standard.
Two 30-pin SIMM slots on an IBM PS/2 model 50 motherboard
A DIMM, or Dual In-Line Memory Module, is a popular type of memory module used in computers. It is a printed circuit board with one or both sides holding DRAM chips and pins. The vast majority of DIMMs are standardized through JEDEC standards, although there are proprietary DIMMs. DIMMs come in a variety of speeds and sizes, but generally are one of two lengths - PC which are 133.35 mm (5.25 in) and laptop (SO-DIMM) which are about half the size at 67.60 mm (2.66 in).
Two types of DIMMs: a 168-pin SDRAM module (top) and a 184-pin DDR SDRAM module (bottom). The SDRAM module has two notches (rectangular cuts or incisions) on the bottom edge, while the DDR1 SDRAM module has one. Also, each module has eight RAM chips, but the lower one has an unoccupied space for the ninth chip; this space is occupied in ECC DIMMs.
Three SDRAM DIMM slots on a ABIT BP6 computer motherboard
256 MB MicroDIMM PC133 SDRAM(Double sided, 4 chips)
A 200-pin PC2-5300 DDR2 SO-DIMM