File size doesn't add up, 2 gigs short

[harry*333]

I have an old white macbook, running OS X 10.4.11
Under "Macintosh HD" in Finder the file sizes are
Application Support- 580kb
Applications - 5.71gb
Developer - 160kb
Library - 3.68gb
System - 1.57gb
Users - 38.85
Total - 49.81gb
Yet it says I've used 52.70gb out of 55.57gb
I downloaded Disk Inventory X but it says the same thing
So is this a miscalculation by OS X or are there some other files somewhere that I'm not adding in my total?

 

[spinnerlys]

Hidden files and directories.
http://www.westwind.com/reference/OS-X/invisibles.html

Have you emptied the trash?

 

[harry*333]

yes my trash is empty

 

[Thiol]

Let me guess, you have 2GB of RAM? Don't forget about the sleepimage file in private/var/vm if you have safe sleep enabled.