1. The why is simple. WinDirStat may not be showing the System Volume Information folder or other things.
More about that at http://support.microsoft.com/kb/309531 DO NOT CHANGE THIS.
2. My best tips are to turn System Restore off then back on.
And find a better folder/file browser. Gyula's Navigator shows things you may miss and the NUMBERS NEVER MATCH when Windows is running. You may find folk that want to get the numbers to match and beyond the 1,000,000,000 bytes is not 1GB there are log files, temp files that come and go so fast.
HP Mini operating Windows XP. Partition Hard Drive 15 GB drive C, 2 GB Drive D. Constantly getting Hard Disk full error on Drive C (14.6GB of 15 GB used). Only have applications, no personal files, pictures, or videos. Can't defrag. Disabled System Restore. Ran WinDirStat and it only shows 8.1 GB on Drive C with 4GB in Windows, 2.5 GB in files, and .8 GB in Program Files. Going to Properties of Drive C from My Computer it shows 14.66GB. Why the disparity between WinDirStat and Drive C Properties? How do I recover the hidden used disk space?
Thanks in advance.