What is it?
To visualize the function of memory in your computer, think of your computer's processor as a worker standing at a workbench. If the worker needs a tool that isn't nearby, he must search for it and hopefully find it quickly. If it isn't immediately available, he may have to turn around and open a locker to get the tool, which takes a little more time. However, if the right tool isn't in the nearby locker, he may have to walk all the way outside to a tool shed to get it, which takes even more time. 

In the same way, your computer's processor needs data to work, but it cannot work efficiently if it has to repeatedly stop and search for the needed data, which is like having to walk all the way outside to the tool shed over and over again for each tool. Computer memory is like the locker and the workbench -- places to store information where the processor can get to it quickly and continue working without pause. Storing more data in memory means it's more accessible and that the computer won't have to slow down as often to go looking for that data. 

Be careful not to confuse RAM (Random Access Memory) with your hard drive. Both perform a storage function and are measured in megabytes or gigabytes. These similarities both contribute to the confusion, but they perform distinctly different functions. Simply put, RAM temporarily stores data while the hard drive permanently stores it. Anytime you save a file, the data is stored on your permanently hard drive. 

What exactly is stored in your computer's RAM? Any open software application, such as a word processor or Internet browser, is temporarily stored in memory. Along with these programs, any data required to operate them is also stored in memory for fast retrieval. More RAM allows your computer to store more data and retrieve it more quickly than with less RAM. With more RAM, you can operate more applications simultaneously on your computer without consuming all its vital resources. 

If there is not enough space available in your RAM, "thrashing" can occur. This is when your computer has to kick out some data from its RAM in order to create space for other data that it needs more urgently. Memory thrashing greatly slows down the computer since it has to wait for the slow hard drive to find the information it needs and load it into memory. More RAM avoids forcing the computer to search the hard drive to find the necessary information. 

The memory used in today's computers usually comes in small rectangular modules that are installed in sockets on a computer's motherboard. There are different types of memory, including FPM DRAM, EDO DRAM, SDRAM, and RDRAM, each of which has its own distinctions and advantages. Most computers only support one type of memory, but some also support two types. 

Why would I need it?
Adding more memory to your computer produces an overall improvement in its performance. It lets the computer run more programs simultaneously, so you can surf the Internet, listen to an MP3 music file, and play a game without slowing down the system. More memory also helps your computer to run complex software even faster, such as recent 3D games or voice recognition programs.