Unless your computer is a real antique, buying RAM means buying DIMMs: dual in-line memory modules. DIMMs come in several types, and which sort you need depends on your motherboard. If your computer's more than four years old, it might take plain old DDR DIMMs (known as "double data rate" because memory can be accessed twice per clock signal). More recent PCs will most likely use the faster DDR2 DIMMs, while high-end desktop systems might use the latest DDR3 standard.
The different types of DIMM aren't cross-compatible: if your motherboard demands DDR2, it won't work with DDR3. To ensure you don't make mistakes, different types of DIMM have notches in different places, making it impossible to plug the wrong sort of DIMM into a slot. To find out which type of DIMM you need, look at the modules already installed on your PC: odds are they'll be labelled either DDR, DDR2 or DDR3. Alternatively, go online and look up your motherboard on the manufacturer's website, or use a system-analysis tool such as SiSoft Sandra (
www.sisoftware.net).
A few motherboards based on Intel's P35 and P45 chipsets provide slots for both DDR2 or DDR3, offering some flexibility. Be warned, though: you can't use both types at once.
If you have a laptop, you'll need to use compact modules known as "small outline DIMMs", or SODIMMs. As with desktop modules, SODIMMs come in DDR and DDR2 flavours, with notches to ensure they're only plugged into the right sort of slot. DDR3 SODIMMs are starting to appear on the market too, though only the very newest laptops use them.
Next: Is there an optimum number of DIMMs?Back to "Memory stripped bare"Author: Darien Graham-Smith
What sort of modules should I choose?