Short answers, pulled from the story.
IBM unveiled the System/360 mainframe computer in 1964. This announcement fundamentally altered the trajectory of computing history by guaranteeing that software written for the first model would run on every subsequent model for decades to come.
The Intel 8086 processor was introduced in 1978. This processor was designed with a specific architectural quirk that allowed it to run programs written for its 8-bit predecessor, the Intel 8080, even though the two chips were not instruction-set compatible.
The PlayStation 2 was released in the early 2000s. This console became a commercial juggernaut largely because it could play games from the original PlayStation, a feature that served as a key selling point during its first months on the market.
The Xbox One backward compatibility program allowed players to rack up over a billion hours with backward-compatible games. This program slowly incorporated support for select titles several years into the product life cycle after the console initially launched without backward compatibility.
The PlayStation 3 removed backward compatibility with PlayStation 2 games to reduce hardware costs and improve profit margins. This decision involved eliminating the onboard Emotion Engine and Graphics Synthesizer hardware chips that were previously used to emulate the older system.