Pat / Bill

The figures for used disk space are usually found on investigation to
understate what is used, although there is at least one factor I know of
that goes the other way.

Windows Explorer records the sum of the files sizes, whereas the size on
disk for some files may be less. The difference is caused where  file
system is NTFS and file compression has been applied. Compressed files
are displayed in Windows Explorer in a blue font. Files not compressed
display in a black font. In the Windows Directory of your C partition
you will have some Uninstall folders in your Windows folder  typically:
$NtServicePackUninstall$ and NtUninstallKB282010$ etc and these in total
can produce a noticeable discrepancy in the figure to be included in any
reconcilaion.

The way to see most hidden files is to go to Start, Control Panel,
Folder Options, View, Advanced Settings and verify that the box before
"Show hidden files and folders" is checked and "Hide protected operating
system files " is unchecked. You may need to scroll down to see the
second item. You should also make certain that the box before "Hide
extensions for known file types" is not checked.

Notwithstanding there remain some files which remain hidden. You still
will not see the System Volume Information folder.
How to Gain Access to the System Volume Information Folder
http://support.microsoft.com/default.aspx?scid=kb;en-us;309531

The contents of the System Volume Information Folder can also be
compressed to produce the same discrepancy mentioned earlier between
file size and size on disk..

Other files  not visible include hiberfil.sys, Norton Protected Storage
and Rollback files.

One way sometimes to discover the existence of larger hidden files is
that they can be revealed in the Most Fragmented Files list in a Disk
Defragmenter Report. Of course the files need to be fragmented to be
seen but those of significant size usually are if the disk needs to be
defragmented. Sometimes these files can be so large there is not
sufficient contiguous free space to be able to totally defragment them.

I would be interested in  seeing a Disk Defragmenter report from Pat's
computer. Open Disk Defragmenter and click on Analyse. Select  View
Report and click on Save As and Save. Now find VolumeC.txt in your My
Documents Folder and post a copy. Do this before running Disk
Defragmenter as it is more informative.

If you unexpected lose a lot of disk space it can be the result of not
stopping logging , although these files are normally visible.