In winxp, I have 4GB of RAM, am using 1.77GB, but programs keep paging out to memory. Why?

"The people at Microsoft have made certain decisions regarding this. It also has to do with Windows being optimized for short (3-6h) uptimes since the majority of users do not use it for longer than that. Linux, for example, uses up all memory and only pages when it is full - but even for this approach there are problems (how to decide what do discard when it does fill up, etc).

Rest assured the pros and cons have been pondered by MS' engineers, and it's not necessarily a bad decision."

One of the common "pagefile" myths is that it is there only for use when physical ram is full. This is not true. As you can see from the wikipedia entry, it is a topic of much more depth than most people seem to realize.