Which PC Memory Module type (SDRAM, DDR, or DDR2) do I need?

Adding more memory to PCs is a cheap and easy upgrade method.

But there are different types of PC memory modules available – SDRAM, DDR, DDR2 – and computers are limited to being compatible with one type only. So you have to know which type you want before buying, especially if buying online.

1) To see how much memory a windows PC has, either run:

Start -> Control Panel -> System

or right click on ‘My Computer’ and select ‘Properties’

The general tab shows the amount of memory:

RAM screenshot

In this case, 192 MB of memory (RAM = random access memory).

2) Look at the existing memory module, which means removing the outer case of the computer, normally held on by a few small Phillips head screws. Power off at the mains beforehand.

Inside there will be a memory module looking like one of these:

Which is held in the motherboard with white edge clips like this:

It’s easy to take that in and out, but for full instructions see Morris Rosenthal’s illustrated guide.

3) The memory module should be labelled with which type it is, but you can tell even without that by looking at the number of small metal pins at the base of the memory module:

SDRAM – 168 pins – 2 notches

DDR – 184 pins – 1 notch

DDR2 – 240 pins – 1 notch

The pins run on both sides of the memory module, so a DDR module has pins 1-92 on one side, and pins 93-184 on the other. Their numbers should be printed beside the first and last pin on each side to save you counting.

November 9, 2007

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