Halo: The Master Chief Collection isn’t just a massive collection of Master Chief’s greatest adventures; it’s also a time capsule that shows just how far the series and video game technology has come over the last two decades. It’s also impressive to see Halo: Combat Evolved Anniversary Edition and Halo 2 running smoothly on Microsoft’s latest Xbox Series X|S consoles, with both games having preserved their original Xbox visuals.

So how did developers 343 Industries and Saber Interactive manage to get legacy game code working on newer Xbox consoles? Through sheer effort, going back to the past, and paying attention to the analyses done by the Halo community. In a Halo Waypoint post, Saber Interactive tech lead Roman Lebedev–who served as lead project programmer on Halo: Combat Evolved Anniversary Edition on Xbox 360–explained how he had to find original Xbox devkit documents and learn how older software worked so that the first two Halo games could have more authentic legacy graphics.