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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).

Error Detection and Correction
Many computers use 8-bit RAM chips, while others use 9-bit chips. The ninth bit is a parity bit for detecting errors. High-end servers and workstations may use error-correcting memory (ECC) and registered DIMMs (RDIMMs). 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. For identification, the notches between the pins are standard. 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. See RDRAM.

Desktop Memory (DIMMs)
To change memory in desktop computers, you have to open the cabinet. 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.