ssd - Why does it seem like I only have 99.8 GB of space, instead of 128?

I have a new Dell laptop with a 128 GB SSD, that came with Windows 8, which I recently updated to 8.1.

When I check my free space it only shows 58 GB of free space out of 99.8 GB.
I have two questions:

1. Why do I only have 99.8 GB of space, instead of 128 GB?


2. What is taking up 30 GB?
   When I sum up my folders on C drive, I only get 29.6 used space, so there are 10 GB "missing".