Apple 13.3 MacBook Air 1.8GHz 2GB RAM 80GB Hard Drive with Parallels Desktop and Microsoft Windows X... PC Notebook "823" Questions

...hardrive is saying its capacity is 24.76 GB yet its supposed to be an 80 gig, It also says i have 823 MB left of free space. It also says used is 23.95 GB. I am wondering where the rest is? some