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Bulking up your computer's memory remains one of the most popular upgrade projects: It's inexpensive, it's relatively easy, and it can dramatically improve performance. And today's memory-hungry software can make upgrading your PC's RAM a virtual necessity. For example, Microsoft recommends at least 128MB of memory for Windows XP; 256MB is better, however, and 512MB is better still.

Most desktop PCs built over the past few years use dual inline memory modules. PC100 (100-MHz) and PC133 (133-MHz) SDRAM DIMMs are most common for Pentium-based PCs built one to three years ago; systems of that vintage based on AMD processors often use PC1600 (200-MHz) or PC2100 (266-MHz) double data rate modules.

Recently, faster DDR modules have become the standard for both Pentium- and AMD-based systems. The most prevalent type is PC2700 (333 MHz), and PCs that use PC3200 (400-MHz) DDR memory are starting to appear. Some high-end computers use dual-channel DDR memory for extra speed. Rambus memory is still available as well. High-performance Pentium 4-based systems often use more-expensive Rambus inline memory modules. Older machines typically have 800-MHz RIMMs, while new systems use 1066-MHz modules.

We get oodles of mail about memory upgrades. Check out "Frequently Asked Questions: RAM Upgrades" for some helpful answers.