| | | | Dual In-line Memory Module. A number of RAM (Random Access Memeory) ICs (Integrated Circuits) fitted to a small PCB (Printed Circuit Board) typically fitted into a connecting slot on the motherboard of a PC. Differing from the SIMM (Single In-line Memory Module) in having a 64-bit path to the memory chips as opposed to the SIMM's 32-bit one. More modern processors such as the Pentium series with a 64-bit bus width require that SIMMs be fitted in matched pairs, whereas DIMMS can be fitted singly. Electrical contacts on either side of the SIMM are redundant (i.e. duplicated) whereas in the DIMM both sides are separate and active. Over time the DIMM has evolved from a 72-pin board using DRAM and EDO DRAM, through 100, 144, 168, 184, 200 and currently 240-pin DDR2 SDRAM and beyond. Part of
the naming convention for DIMMs includes the data width of the chips used in bits - this is usually shown in the form "x4" (by 4) or "x8" (by 8) for example - it refers to how the memory controller addresses the ICs, for example a 72-bit memory controller will need to address both sides (Ranks) on a 36-bit x4 board at the same time whereas with a 72-bit x8 one it only needs to address one side at a time to access or write data. Data rates have
increased from a mere 66MHz PC66 to PC2-6400 with an 800MHz data rate and more. Likwise the form factor of the DIMM has changed to match that of the hardware it is being fitted to: initially as much as 1.7" high, the size of the PCB has been shrunk over the years, driven partly by the server market, so that now DIMMS a mere 18.3mm high are used in many blade servers. | | | |
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