Here’s some links you may want to read:
http://answers.microsoft.com/en-us/windows/forum/windows_7-hardware/windows-7-sp1-64-bit-only-recognizes-746gb-of-3tb/7737adf3-e4c2-46eb-b67b-0dbbe60c84bes
http://www.pcmag.com/article2/0,2817,2373641,00.asp
http://www.anandtech.com/show/3981/western-digital-caviar-green-3tb-and-my-book-essential-3tb-drives-reviewed/2
http://www.rodsbooks.com/gdisk/booting.html