How big the real space is for the hard drive?Why 1T only 931G?

I have bought one WD element SE 1 TB, But when I  first use and look up the property it shows that there is only 931G free and used space is 208M,  It lacks so much space and I doubt if it is real. Why? Could anyone explain it? and how about other kind of hard drives with different space? How real big  is the 750G? And how about 500G? looking forward to help, thanks in advance.

Hi it is the way windows reads the size have a look at this link for a explanation.

This knowledge base article explains why the drive appears to have a smaller capacity than what it actually has.

Drive displays a smaller capacity than the indicated size on the drive label