Which of the following operating systems supports full usage of 8GB DDR3 RAM?

A.
Windows 7 Professional x86

B.
Windows 7 Home Premium x64

C.
Windows XP Professional

D.
Windows Vista Home Premium x86

Explanation:
http://www.tomshardware.com/answers/id-1677684/12gb-ram-installed-8gb-showingwindows-ultimate-x64.html