Windows 10 build 9697

This pre-Technical Preview build of Windows 10 is the earliest known as of 2016-05-31. It was shown at the /BUILD/ on 2014-04-02. Rather like Whistler build 2202 and Windows 7 build 7700, there is a dispute as to whether it is a Windows 10 pre-release or a Windows 8.1 post-RTM (even the build string calls it 'Windows 8.1 Enterprise'.)