Why MY 1TB external hard drive is only 749GB.

I have WD 1TB external hard drive and I partioned it for PS3 and justs storing files. I do not use Timemachine. I wanted to be able to plug in to PC and transfer files.

I just realized that I only 749GB of space, of which 680GB is for Ex-FAT and 69GB for MS-DOs(FAT). I am not sure why do I only have 749? How can I get my 250GB?