CPU-Z is your go-to program for identifying RAM.
Random Access Memory (RAM) is the memory that Windows uses to temporarily store data. It stores some data on your hard drive, but RAM is preferred because it works much, much faster for storage and retrieval. The more RAM you have, the less Windows will use your much slower hard drive for temporary storage. However, many different kinds of RAM are available, only some of which is compatible with your particular computer.
Consulting the manufacturer
Windows doesn't have any built-in function to show you what type of RAM you have, only how much. To find that out, consult your computer's documentation. If your documentation is not available, go to the manufacturer's website and search for your model number in the support section, if this is a pre-built computer.
To obtain the model number, right-click on "My Computer" (or just "Computer" in Windows Vista) and select "Properties." You will see a large company logo in the bottom left of this window and the model information in the lower-right. If you have built this computer yourself, however, you will need to consult your motherboard documentation.
Some manufacturers do not have comprehensive websites, however. In that case, you may need to contact them by phone
What to do with the information
So you have identified your RAM at this point. You know how many slots it's occupying on the motherboard. With these two pieces of data, you can figure out what kind of RAM you need to buy. Sometimes all RAM slots are already filled. So to get more RAM, you have to take one stick out and replace it with a stick that has more memory. Make sure that RAM sticks are securely in their slots when installing; they will "click" into place.
For example, let's say you have two gigabytes (GBs) of RAM taking up all four of your RAM slots. That means each stick contains 512MB of RAM. And you want to expand to 4GB of RAM. The easiest way to do that, then, would be to replace one 512MB stick with one 1GB stick, and replace another 512MB stick with a 2GB stick. (This technically gives you a total of 4096 megabytes of RAM instead of 4000 megabytes -- some industry computations will vary from "real world" calculations.)
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