As early as 2014, Microsoft introduced Windows 10’s Windows Technology Preview program. It was later officially named the Windows Insider program and was released to the public to help Microsoft conduct internal testing before the official release of the operating system, allowing it to get user feedback on the operating system.
Now it looks like Microsoft had this idea 20 years ago. When Windows 95/98 became popular, Microsoft was developing an operating system called Windows Neptune. According to a recent tweet from Albacore, Microsoft also had an almost operational Insider Tester program that, judging by its appearance, was actively using it to test Windows updates. As early as 1999, Microsoft used a self-hosting mechanism to provide testers with new updates without having to use an ISO file formatting system.
Microsoft released developer and consumer previews for the operating system at the time, and these near-completed versions were almost complete with few errors. Unfortunately, Microsoft didn’t end up releasing the Windows Neptune operating system, but it helped Microsoft develop the Windows Update features used in modern Windows operating systems.