A DIMM (dɪm) (Dual In-line Memory Module), commonly called a RAM stick, comprises a series of dynamic random-access memory integrated circuits. These memory modules are mounted on a printed circuit board and designed for use in personal computers, workstations, printers, and servers. They are the predominant method for adding memory into a computer system. 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 and laptop (SO-DIMM) which are about half the size at .
DIMMs (Dual In-line Memory Module) were a 1990s upgrade for SIMMs (Single In-line Memory Modules) as Intel P5-based Pentium processors began to gain market share. The Pentium had a 64-bit bus width, which would require SIMMs installed in matched pairs in order to populate the data bus. The processor would then access the two SIMMs in parallel.
DIMMs were introduced to eliminate this disadvantage. The contacts on SIMMs on both sides are redundant, while DIMMs have separate electrical contacts on each side of the module. This allowed them to double the SIMMs 32-bit data path into a 64-bit data path.
The name "DIMM" was chosen as an acronym for Dual In-line Memory Module symbolizing the split in the contacts of a SIMM into two independent rows. Many enhancements have occurred to the modules in the intervening years, but the word "DIMM" has remained as a generic term for computer memory modules.
Variants of DIMMs support DDR, DDR2, DDR3, DDR4 and DDR5 RAM.
Common types of DIMMs include the following:
DIMM
100-pin, used for printer SDRAM
168-pin, used for SDR SDRAM (less frequently for FPM/EDO DRAM in workstations/servers, may be 3.3 or 5 V)
184-pin, used for DDR SDRAM
200-pin, used for FPM/EDO DRAM in some Sun workstations and servers.
240-pin, used for DDR2 SDRAM, DDR3 SDRAM and FB-DIMM DRAM
278-pin, used for HP high density SDRAM.