i was cleaning up thumper and came up with  
this  off topic question, but since we are such a diverse (or is that perverse)  group i bet someone's got the answer.

why does my computers "c" drive show 17 gigs used.
when i add it up it only comes to 10 gigs.

i first noticed the missing space with "98" it got more progressive in "m.e" and now with "xp" it's huge.  these are different machines not upgrades to same

in view options i even told it to show "hidden" files so i could add those up also..

any answers.  and remember to keep the explanation in lay terms.. i'm not the sharpest tool in the shed.  

That's somewhat true, but real the reason that you see more "used space" than what you expect from your math results is because of virtual memory and what Windows calls a paging file.  

A paging file is a section of your HDD that Windows reserves and uses as RAM (mine currently says that I have a paging file size of 720 MB)

If you go to your control panel, and click on "System" you will get a window called "System Properties".  Then click on the "Advanced" tab at the top.  Now you see an option called "Performance" and a button called "Settings".  Click that for "Performance Options" and at the bottom is "Virtual Memory".  There is your explanation....you have a button called "Change", but it is better to just let Windows manage this space.

You haven't lost the space, it's just that Windows XP is reserving that space for system functions.....

Click safe