Memory which is better known as RAM which stands for Random Access Memory, the term Random comes from the fact that the Processor or CPU can access information from any individual location or memory address within the RAM. This is what is termed volatile memory used to temporarily store information for processing. It is the most common and fastest type of memory used in computers and is also the most expensive. The memory can be overwritten with new information over and over again.
It is the place inside a computer where software, such as the Operating System, applications or programs and also data that is in current use are stored so that the processor can access the files quickly. RAM is used for this task because it is much faster to both write to and read from than the other types of storage that you will find inside the PC such as the Hard Drive CD Rom or indeed a floppy disk.
All the data that is stored in RAM will only stay present until the computer is turned off. Once the PC is shutdown the RAM no longer holds tha data. If your PC is running a little on the slow side, doesn't seem to respond quite as quickly as it used to then there is a good chance that you need to increase the amount of RAM memory that is inside the box.
There are so many different types and makes of memory, it can be difficult to know just which memory module to buy, what size how many pins etc. The best thing to do in this case is to go to a company that will help you find the memory chip you need. The website, run by crucial memory has a useful little tool that will scan your computer and tell you which memory you are using and therefore which memory you need to upgrade. Screenshot below.