Back when memory cost $50 per megabyte, we advised people to install as much memory as they could afford. With memory now selling for pennies per megabyte, we advise people to install as much memory as their motherboards will accept.
How much memory you actually need depends on the operating system and applications you use, how many windows you keep open, which background services and processes you run, and so on. Memory is more important than processor speed when it comes to system performance. Windows XP runs faster on a slow Celeron with 256 MB than on a fast Pentium 4 with 64 MB.
Using a big swap/paging file cannot substitute for having enough RAM. Windows virtual memory allows you to run more and larger programs than fit into physical memory by temporarily swapping data from RAM to a disk file. When Windows swaps to disk, performance takes a major hit. If your hard disk clatters away every time you switch between running applications, that’s a sure sign that heavy paging is going on and that your system needs more memory. RAM is cheap. Install enough of it to minimize use of the paging file.
To determine how much memory you need, choose the following category that best describes your usage pattern. If you fall between two, choose the higher. Note that newer versions of applications usually require more memory.
Web browsing, email, casual word processing and spreadsheets, checkbook management, and simple games; one or two windows open; particularly ...