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Random Access Memory (RAM) is the storage area your computer uses for programs and data while it's running. More RAM speeds computer performance and allows different programs to run at the same time. Generally speaking, the more RAM your computer system has, the better. In fact, adding RAM is one of the cheapest ways to improve your computer's performance.
The important thing to remember about RAM is that it's temporary. It's used by the CPU (Central Processing Unit) to hold the operating system, active applications and any open files. Once the computer is turned off, the information stored in RAM is gone.
One main benefit of RAM is speed. When you open a  software program or enter data into your computer, you're placing this information in your computer's RAM. As you continue to work, your CPU constantly updates the RAM with new information.
If all of these changes were stored on your computer's hard drive while you worked, it would take forever to get anything done: Reading information from and writing data to a hard drive is much slower than shoveling the data into and out of RAM.
Of course, RAM is only temporary memory. You need to save your work -- on a hard drive or other storage device -- every so often to protect your data from a power failure or a system crash. Once you turn off your computer, all of the information stored in RAM is lost.
Most computers come with RAM pre-installed on their main circuit board. The amount of RAM installed on new PCs ranges from 128 megabytes to 2 gigabytes. If you're buying a new computer, get one with at least 512 megabytes of RAM. 1 gig is even better.
To increase the amount of RAM in your computer, you'll install additional memory chips in RAM expansion slots on the main circuit board. These chips come in memory modules called SIMMs (Single Inline Memory Modules) or DIMMs (Dual Inline Memory Modules). Memory modules also come in different pin configurations, and you must use the right type of RAM for your computer's expansion slots. SIMMs come with 72-pin interfaces, while DIMMs have 168-pin designs.
Laptop computers use completely different RAM modules than those used for desktop computers. While desktop machines use industry-standard modules that will work in any computer, laptops often use proprietary modules which will work only in that type of PC. For that reason, laptop RAM is much more expensive.
If you know exactly what kind of RAM to buy, you can easily install new modules yourself. If you aren't sure or don't want to tinker with your computer's innards, bring your computer to the store. Many dealers will install memory at no additional charge, or for a nominal fee.
The most common type of RAM used in memory modules is DRAM, for Dynamic Random Access Memory. One of the most important characteristics of DRAM is its speed. The time it takes a CPU to access information stored in RAM is measured in nanoseconds, abbreviated "ns." A nanosecond is a millionth of a second. DRAM generally boasts access speeds in the 60- to 80-nanosecond range.
Newer computers use a faster type of DRAM called DDR (Double Data Rate) memory. You can't mix-and-match. Always make sure the RAM you buy matches the type in your computer.
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