Now that you have an idea how much memory you want to get, you’ll need to do a little bit of research to make sure that you get exactly the type of memory that works with your motherboard. This is extremely important for several reasons:
Some motherboards are very specific about the type of memory. This is especially true for some name-brand machines like Compaq, Dell, Gateway, etc. A lot of times they don’t work with generic memory.
Each memory slot usually has a limit regarding the size of the memory module installed. You don’t want to buy a 256MB module just to find out that the motherboard only supports up to 128MB per slot. However, such a limitation can usually be corrected with a BIOS upgrade.
Compatibility is an issue when you plan to mix and match the new RAM with the existing modules. Sometimes they don’t play nice unless they match.
Consult your system documentation or the vendor to find out exactly what type of memory is currently in your machine. If it’s a Pentium II or newer machine, most likely it uses 168-pin DIMMs, which looks like this:
If it’s a first generation Pentium or older machine, it probably uses 72-pin SIMMs, which look like this:
Be sure to dig up a copy of the motherboard manual so you can read up on the exact memory requirements. This is important because you need to know if the motherboard has any special requirements or limitations as mentioned above. If you don’t have the original paper copy of the manual, chances are that you can download it from the manufacturer’s web site.
Adding Or Replacing?
You can go one of two routes:
Adding memory – If your existing memory is good, then you might want to consider just adding an additional stick. For example, you might have currently 64MB of PC-100 SDRAM, and want to add another stick of 64MB PC-100 SDRAM to make it 128MB total. Nothing wrong with that. The only caveat here is that you should make sure that the additional memory can coexist peacefully with your existing RAM.
Replacing memory – If your existing memory is old or slow or minuscule, you might want to consider trashing it and replacing it with a completely new set.