To understand the significance of Build 7989, one must understand the timeline. Windows 7 had been a resounding success, released in 2009. By 2010 and early 2011, Microsoft was deep in development on the next iteration, codenamed "Windows 8."
In the enthusiast community, "unlocking" hidden features in unreleased builds is a popular pastime, often referred to as taking the "Red Pill" (a reference to The Matrix ). Build 7989 is famous for requiring these tweaks to reveal its secrets. windows 8 build 7989