Memory

Every time you open a file or run a program, the computer loads commands and data into RAM (random access memory) chips located on memory modules mounted in sockets on the motherboard. The CPU exchanges data with these modules millions of times every second. When you save a file, the computer transfers the data from RAM to permanent storage on the hard drive or some other media.

In Windows and other modern operating systems, the CPU is often running one or more programs in the foreground and many other utilities and services in background. The computer is constantly moving programs and files between the RAM and a section of the hard drive reserved for use as additional virtual memory. Because the CPU can read data from RAM modules much more quickly than it can retrieve it from the mechanical, or hard, drive, a computer processes data faster if it has more RAM. Adding more RAM is often the single most cost-effective way to improve a computer's performance.

CROSS-REF 

Chapter 7 explains how memory works with the other components inside your computer, how to buy and install additional memory, and how to test your computer's RAM.

The specifications supplied by the manufacturer or dealer for every computer always includes the amount of RAM installed on the motherboard. The amount that your computer actually needs depends on the demands of the operating system and the application programs you expect to use. For Windows XP, the computer should include a bare minimum of 256MB; for better performance, increase the amount to at least 512MB or even 1024MB. For Windows Vista, the practical minimum is probably about 1024MB.

Those are minimums. For audio or video editing, graphic design, or other work that involves very large data files, and for games, adding an extra 512MB or more of memory makes the computer significantly more responsive and reduces the time necessary to open and close files. Even on less-demanding applications, additional memory can make a noticeable difference. In most cases, you can see a greater improvement in the computer's performance after you add more memory than with a faster CPU. But don't get carried away with adding memory. There's a point of diminishing returns where more memory doesn't make any more difference.

How Much Memory?

It's easy to become confused by the way memory size is described, because the names for large numbers of data bytes are based on multiples of 8. Therefore, 1 kilobyte (KB) is 1024 bytes (8 × 128), rather than 1000 bytes, 1 megabyte (MB) is 1024 kilobytes, and 1 gigabyte (GB) of memory is actually equal to 1024 megabytes. The most common sizes for memory modules are 256MB, 512MB, 1024MB (1GB) and 2024MB (2GB).

If you order additional memory along with your computer, instruct the dealer to install the new modules and test them in your system before they turn it over to you. Don't accept the loose modules as separate pieces that you have to install before you can use them, because loose modules may not have been tested before they were shipped to you.

If you add memory to an existing computer, run a memory test such as Memtest86 (available from http://www.memtest86.com/) after you install the new modules. If the test identifies any problems, remove the new modules and return them to your supplier for a refund or replacement.

Some types of memory modules must be installed in matched pairs. The manual for your computer or motherboard tells you if your system has this requirement.