Herp derp, does installing something take up space? Maybe it goes into a black hole and everything is run off the CD. Of course your going to have space missing when you install an OS. Windows 7 takes up alot especially ultimate. If your page file is automatic and it set it to 1-2x your ram if you have more than 8 gb it will take up 8-32gb of hard disk space just for the page file.