For a low-cost, potentially dramatic boost to your system's performance, nothing beats adding memory. And there's never been a better time to do it: RAM prices are amazingly low (about $25 for 128MB at press time), and applications and operating systems continue to demand more and more of it. For Windows XP alone, 128MB is recommended. Add a few concurrently running applications, and it no longer seems ridiculous to equip your PC with 256MB, 512MB, or even more.

Adding RAM makes your PC work better because it makes data instantly available. If you start a task and your PC has insufficient unused RAM to handle the job, Windows copies a dormant task to a swap file on your hard drive, freeing RAM for the new task. Switch to a swapped-out task, and Windows makes it trade places with some other dormant task, causing a significant performance hit.

Most recently made PCs use Dual Inline Memory Modules to hold RAM. Most common are PC-100 (100-MHz) and PC-133 (133-MHz) SDRAM DIMMs. Newer systems based on high-speed AMD processors use PC2100 DDR (double data rate) SDRAM, which runs at 266 MHz. Some Intel-based PCs instead use more expensive Rambus modules (called RIMMs), available in speeds up to 800 MHz.

If your PC is four or five years old, it's probably designed for 66-MHz SDRAM, but you should still be able to use 100-MHz or 133-MHz SDRAM modules. Although they won't work at full speed, they remain the best value. Some older computers use Single Inline Memory Modules for RAM. We show DIMM installation here; SIMMs pivot into their slots and must be installed in pairs.

Stan Miastkowski is a PC World contributing editor.

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