With windows 8 and 8.1 having a low acceptance rate, most users prefer to downgrade their system to windows 7, been a popular and widely accepted OS after the Windows Vista disaster. This is ideal if you purchase a license key or reformatted your PC and will like to get an ISO copy of the genuine version of Microsoft OS. Windows 7 – 32bit and 64bit in the following versions professional, ultimate, and home premium can be downloaded on the official page of Microsoft approved site.