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Definition: memory module


A narrow printed circuit board that holds memory chips (RAM chips). The common architecture for desktop computers is the dual in-line memory module (DIMM). Because of space limitations, laptops use small outline DIMMs (SODIMMs). The modules have notches in different places so that they cannot be inserted into the wrong slots (see illustration below). See RAM.

Error Detection and Correction
Many computers use RAM chips that hold eight bits per byte, while others have nine bits. The ninth bit is a parity bit for detecting errors. High-end servers and workstations may use error-correcting memory and registered DIMMs (see ECC memory and RDIMM).

Upgrading Memory - Read the Manual (RTFM!)
A single DIMM can often be used, but pairs of DIMMs increase performance in machines that support dual channel DDR SDRAM. When upgrading memory, read the motherboard manual to find out which module combinations can be used. See SDRAM, memory types, memory card and Hybrid Memory Cube.




DIMM Modules
DIMMs are used in desktop and servers; laptops use SODIMMs. The notches at the bottom of the modules designate the number of pins. However, the way chips are placed on the module is up to the manufacturer.






Earlier Modules
RIMM (Rambus) and SIMM modules are no longer used. RIMM modules transferred data over 16-bit and 32-bit channels, whereas SIMMs were 32-bit. DIMM modules support 64-bit paths. See RDRAM.






DIMM Modules in a Desktop Machine
To change memory in desktop computers, the cabinet has to be opened. Two of the three DIMM slots on this Mac motherboard are empty.






Laptop Memory (SODIMMs)
To change laptop RAM, a cover plate on the bottom of the unit typically has to be unscrewed.






Two Sticks of Memory
RAM modules are often called "sticks" because they are housed on long, thin circuit boards.