Both Crucial and Kingston have applications on their websites that allow users to figure out what type of RAM your system needs, either by entering in the make and model of your notebook/desktop, or by running a little desktop application that will scan your computer’s hardware configuration. Of course, both of them are designed to sell you the RAM after you scope out your system, and you can buy online right then and there. But if you copy the information down (is it DDR? DDR2? SDRAM? How many slots does the system have? And what’s the maximum capacity recommended by the application?) you should be able to take it into your local computer shop and buy the RAM your system needs.