Several news outlets reported the discovery of a 1970s Fourth Edition Research Unix magnetic tape at the University of Utah in July 2025 and its successful restoration. This is a significant find, because up to now only the Fourth Edition’s manual was thought to have survived. Over the past few days I incorporated the tape’s source code into the Unix History Repository hosted on GitHub (see it here) and studied the code’s composition. The Fourth Research Edition Unix came out of the famous AT&T ...