Typical Memory Module

Memory modules are small circuit boards which temporarily store programs and data that is being used by the CPU (your computer's processor).  When you open Wordperfect, for example, the program is actually loaded into the system memory.  When you create a document, it is also stored in the memory until you save it to disk.  If the program requires more memory than you have installed on your computer, or if you are "multi-tasking" and running several programs at once and all the memory is in use, Windows will use a temporary memory storage area on your hard disk called a "swap" file to hold the data overflow.  You can check the amount of memory installed on your PC by right clicking the "My Computer" icon, then select "Properties" from the drop-down list. 

Since the price has dropped so drastically over the past few years, you should pack your system with lots of memory, but be sure to buy the right type!  There are dozens of different types of memory available now, and some of it will not be compatible with your system.