A reader dropped a comment onto another page with a question that I’ve asked myself many times…

I wonder if you can help with this perhaps related problem. Running Windows Vista, it reports the hard drive has only 58 MB of free space. Adding up the folder sizes as shown in the properties window for each folder in Windows Explorer (including hidden folders), indicates that there are hundreds of GB of unused space.
When the limit is reached and there is no space left, by Windows reporting, no files can be saved.
It seems obvious that Windows’ reporting is faulty, but as it stops the saving of files, it cannot be ignored.
Any solution / suggestions?

Unfortunately, it’s not likely that Windows is simply lieing to you. More likely is that your technique of evaluating the disk space used by each folder is flawed. However, just to make sure Windows isn’t lieing, you can run a checkdisk at an administrative command prompt by following these steps (after the jump):

1. Click Start and type cmd.
2. Right-click cmd.exe and then click Run As Administrator.
3. Type chkdsk C: /f /r and then press Enter. I’m assuming the free disk space problem is on your C:\ drive, but you can check any disk this way.
4. When prompted, type Y and press Enter.
5. Restart your computer and be patient while Windows scans your disk.

After you restart your computer, check your free disk space again. If your free disk space still isn’t where you expect it, then it really is being used by something. First, use the Windows Disk Cleanup Wizard to remove unnecessary files.

The trick is finding the files and folders that are using the space. Windows isn’t especially good at this, but there are many free tools that are good at it. My favorite is the free and tiny Scanner disk space usage analysis tool. Download and run the .exe file–no install necessary–and then examine the radial chart to find the folders using the most space. Hover your cursor over the bigger sections of the diagram to find the folders using up lots of space. If you don’t expect that folder to use that space, right-click the section and then click Open. Scanner opens an Explorer window to show you the contents. As you can see from this screenshot, my Shared Virtual Machines folder is using 17 GB–a surprise to me, since I don’t use that folder to store virtual machines anymore.

I managed to clear up about 40GB of unneeded files, postponing the purchase of more hard disks by another couple of months…