I have a 100 GB hard drive that Windows XP says only has 8 GB of free space. When I calculate the amount of disk space used it only adds up to 40 GB. I've included all hidden and opererating system files in this calculation. There is about 40 GB of space unaccounted for. Any ideas what might be causing this problem? Seems to be a bug in the OS.

No bug. Run chkdsk and post the results

How are you obtaining the numbers that you're adding up? "So won’t you give this man his wings What a shame To have to beg you to see We’re not all the same What a shame" - Shinedown

I pointed to each directory and looked at the properties. That gives you a size for the directory plus all it's sub directories. I also tried a program called treesize and got exactly the same results. If it was just a gig or two, no big deal, but this is almost 1/2 the hdd that's not usable. Windows reports the size of the hdd correctly but the available disk space is where the problem shows up.

Did you run chkdsk? Do you have System Restore enabled? Is there only one partition? "So won’t you give this man his wings What a shame To have to beg you to see We’re not all the same What a shame" - Shinedown

I have run chkdsk, no problems were found. There is a small recovery partition and also the main partition which is reported as 88 GB. System restore is on. I have checked to see how much disk space system restore is using I thought that might be the problem. The folder where restore points are stored is called the System Volume Information folder. It was only using about 6 GB. I've researched this problem quite a bit online, tried a lot of different suggestions to find out where the disk space is being used and I can't figure this one out. This is a Windows Xp pro load on a thinkpad notebook. The OS load was factory installed, the machine is virus free, no addware or other garbage. The OS sees the drive correctly, reporting it's size as 88 GB. Actual disk usage with my calculations and also the treesize program is at about 40 GB. Explorer tells me there is only about 8 GB of space left. STRANGE! If all else fails I might just try reformatting the hdd, reloading the OS using a Microsoft disk and eliminating any unnecessary Lenovo stuff. I would think that would fix the problem but I'm not even sure that will do it, plus I would prefer not to have to reload everything. Thanks for the help, Ken

So where is that post of the chkdsk results screen? Have you defragged? While you are at it post a screen shot of Explorer that shows the 8gig being free. We need to see numbers to diagnose the issue. Guantanamo bay is a National Disgrace! End it NOW!