Like this one: http://www.ebay.com/itm/Microsoft-Windows-7-Ultimate-64BIT-Operating-System-Software-DVD-/111037041775?pt=US_Operating_Systems_Software&hash=item19da52cc6f Not OEM the full version of Windows. I use my friends PC It's a Acer Aspire AT3-605-UR21 Intel Core i7 4th Gen. 3.4GHz 12 GB 1TB Desktop PC... Anyway every time I format it from time to time. And I use the COA sticker that came with my desktop. I activate easily. If I buy the full retail full version of Windows and will it come with a 25 digit key sticker were I can stick the COA next to my other COA key and use that 64 bit key to install Windows 7 Ultimate 64 Bit from time to time, I like to format my computer cause sometimes viruses, or I end up messing up the files.