ACE Util. it's a program that can be downloaded here:
http://www.acelogix.com/.
Nice soft
Problem is, what U are looking at? When U choose properties of all folders,
on your system partition, from the popup menu. U should look for 2
positions:
1. Size
2. Size on Disk (I'm not sure if it sounds like a say, I have a polish
system, but the context is similar)
Ad1. This is a real size of your file.
Ad2. Depends on your file system (FAT32, NTFS, FAT and so on). For example U
have on your HDD clusters 4kB, and you have a 1 kB file to save, the real
size of it is 1kB, but on your hdd U have to write it into one cluster
(4kB), and then U have only one file for one cluster, so these 3 kB are
marked as "written" and they are logically "lost". There are some 3rd party
tools that can change this what U are talking about: real size= logical
size, during formatting change the size of cluster:
http://support.microsoft.com/default.aspx?scid=kb;EN-US;q314878
Quite tricky, there is another situation, which U may be interested in:
producers use to tell about unreal capacity, they count: 1000B=1KB,
1000KB=1MB and1000MB=1GB and so on. U know that is like this: 1GB to
it's1024MB, MB it's1024KB...
So when U have 40GB HDD it means, that U have 39062500KB = 38146,9MB = 37,2
GB.
Remember that paging file (if U have default it is: 768MB) and other
important system files are hidden. PF is not included into the size report
in properties. So if U think that U can f.ex. 768 mb free on your system
partition, and U see the message that U are running put of space, dont worry

then U will know what is going on

.
Hope it helped.
Paula Januszkiewicz