Native pure version operating system is the best. For sale, Microsoft officially doesn't provide downloads, but as we all know, people in China are eclectic, so you can download all the operating systems and software of Microsoft from this website established by China: msdn.itellyou.cn. It's all pure versions. If you install them, Baidu will do it. As for the official OEM version of the operating system, it was modified by the dealer, which is not optimal, but it is in the best interests of the dealer. To download win7, go to: Operating System -windows7- Simplified Chinese -windows7 Ultimate with Service Pack 1, download 2G memory X86, download 4G memory X64. hope this helps