I recently had a friend point out something strange about his C drive space, and checking my own, I noticed that I have exactly the same puzzle.

We're running Vista Home Premium (this isn't a problem on my second desktop running XP) and if the individual folders are selected and right clicked, properties will show the total size as being around 25 GB less than Explorer gives as being used space. For instance, my C drive says (roughly) 37 GB free out of 80 GB, but totalling the individual folders gives 26 GB, which ought to mean 54 GB was free. It seems that Vista is hiding something that selecting "view hidden folders" still doesn't show. I don't see system restore anywhere, but then I'm not sure absolutely sure where Vista stores it or what it's named. And surely if you select to view all folders everything on your PC should then be visible? I wouldn't have thought 25 GB was put aside for system restore anyway, if I knew that I'd change it straight away!

Has anyone else noticed this or have any idea what the cause could be? It's too large an amount to be explained in the rounding up of bytes and like I say, doesn't affect the C drive in my computer running XP.