Desktops: Can someone tell me what virtual memory is?

English Answer Here, Finally!

It seems people replying to this post ''say'' everything, except to answer the original question. So here goes:

1) When a program runs, it has to ask Windows for ''chunks'' of memory when it needs to store something.

2) Other programs also do the same thing, and there's only so much memory.

3) If there's not actually enough memory (RAM) to satisfy the request (1), then Windows has a ''Plan B'': it finds a chunk of memory that hasn't been used for a long time, and copies it out to the disk, then gives it to the program that asked for it.

4) Eventually, the program that ''owns'' the memory that got copied out in (3) may want to use it. Then, Windows will find another ''old'' chunk of memory, copy IT out to the disk, and copy the chunk from (3) back in.

And so on. Since disk speeds are measured in milliseconds, and memory speeds are measured in nanoseconds, which are a million times smaller, you can see that doing this much will slow down your machine. Amazingly, a desktop machine can tolerate a fair amount of paging/swapping (used synonymously) without appearing to slow down much to a human observer. On the other hand, laptop hard drives are typically 3 - 4 times slower than desktop drives (for lower power usage), so it's a much bigger problem on laptops.

When you get that message, it really "just" means that Windows is increasing the size of your page/swap file. Unfortunately, programs that request more memory while it's doing that can get errors, instead. (I have no idea why that seemed like a good idea.)

The simple solution is to stick more memory in your PC. Unfortunately, no matter how much memory you have, and how little you need, XP will still swap some. Please don't ask me why: other Operating Systems don't, but we're talking about Windows here.

An even simpler (and free) solution is to try configuring the ''initial page file size'' to the size yours normally is. That way, you won't get the obnoxious message (and possible errors) while Windows increases the page file size. Also, to add insult to injury, when it increases the page file size, it almost always ''fragments'' the file, storing the new part on a different place on the hard drive from the old part(s), which makes it even (much) slower to access. (Double bad.)

So, how much swap space do you need? You can tell how much memory you're using currently if you fire up Task Manager, and look at the ''Commit Charge'' (at the bottom). Then subtract the physical memory (RAM) size, listed on My Computer->Properties->General, and you have the (very) approximate amount of swap (page) file space you need right now.