windows 7 - Why is the folder size (in properties) different from the total file/folder sizes in the folder?

Here's my problem

I'm trying to do a cleanup of my hard drive, and I'm constantly seeing this scenario:

(1) Aggregate folder size: I check the folder size viewing properties right clicking the folder

(2) Individual folder/file sizes: I check the individual file/folder sizes belonging to that folder viewing properties on the individual file/folder sizes, and then adding them up (with hidden and system files shown).

These two figures are always different, sometimes by a large margin.

For instance, my C drive now, by method (1), shows a consumed space of 42.4 GB.

However, by method (2), by inspecting the respective files/folders, the total consumed space adds up only to 33.1 GB. This is a 28% discrepancy (over the smaller file size) and I have no idea where the rest of the space is going.

My hard drive is constantly in danger of being full (it's bootcamp on a mac with 50 GB of partitioned space), and there's not much I've got installed in terms of software, nor do I have large media files like movies, downloads, temp files, application temp files, torrents, etc.

Most of it's just consumed by the files in C:/Windows, but last I checked, I don't know enough to know which files to delete, and I've heard that you really can't do anything about the space boggling winsxs and system32.

Can you guys recommend a starting point to free up disk space?

Thanks!!

Baggio.

Answer

When you open Explorer and select properties, Windows reads the free space from the NTFS bitmap metafile. Selecting all files/folders in explorer and showing properties, scan all files/folders. But Windows skips here hidden files/folders and folders where your current user doesn't have read permissions (System Volume Information folder for example).

You should use TreeSizeFree (run it as admin) to see which folders take most space: