Here is a great resource for Windows previous versions documentation thanks to Great Lakes Geek.
Are you running an old version or Windows? If you are searching for previous documentation, this site has content for older products or services, such as release notes, deployment guides, and how-to articles. It’s the archive of all Win7/8, Windows Server 2012/2008/2003, R2, etc. info previously in TechNet.
Unfortunately that legacy content isn’t searchable as of now from Google or Bing. But it is searchable on the archive pages.So if you’re looking for specific information (like Windows 8.1 release notes or how to repair a Windows image), you can use the Search box to search all of the older Windows client libraries.