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DIMM Memory Modules

What is a DIMM?

DIMM stands for Dual Inline Memory Module: it is a plug-in circuit board containing multiple RAM chips which clips into a socket in the computer's motherboard. The RAM socket is connected to the CPU via the MCH (Memory Controller Hub - aka Northbridge) chip on the motherboard, which allows traffic to flow between the two.

A SO-DIMM is a more compact DIMM that is almost exclusively used for laptops, whereas the standard DIMM is used in desktops.


Identifying a DIMM

The DIMM is small, rectangular circuit board, roughly 135x30mm in dimension, containing several large RAM memory chips. The photo below shows a 240 -pin DDR2 DIMM:

A typical DDR2 memory DIMM

On the bottom edge are a number of gold plated connectors: for desktop DIMMs, 240-pins is the norm these days but SO-DIMMs are smaller and have less pins. The connector edge is slotted (-in the photo above, the notch is near -but not exactly at- the centre of the connectors): this is important, as it stops you slotting in the wrong DIMM type (-or attempting to put the right DIMM in the wrong way around).

On the shorter edges are two notches per side: when the DIMM is inserted into the socket correctly, then pushed down, clips attached to the slot ends clip into these notches and lock the DIMM in place. The photo below shows a motherboard with two (DDR3) DIMMs in place on the motherboard:

DDR3 DIMMs in position on the motherboardNote that in this photo:
  • The motherboard sockets can be seen as a light blue colour in the photo (-but they could be one of several colours)

  • The notch position in the socket is indicated by an absence of slats in the socket edge (-again, it's near the centre of the socket, but slightly nearer the bottom than the top)

  • The white end clips are shown secured into the slots in the DIMM ends


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