It is well known that id Software's Commander Keen technology was originally designed to support a PC port of "Super Mario Bros. 3," with John Romero releasing a proof-of-concept video in 2015. Although Nintendo did not adopt it, it was groundbreaking in bringing smooth screen scrolling to PC games.

A copy of that Mario demo was found, seemingly at random, in a submission to the Strong National Museum of Play. Andrew Bowman, the museum's curator of games, told Ars Technica that the disc was from a larger piece submitted by an unnamed game developer. This developer was not involved in the demo, but received the demo "on the job."

"I didn't expect to see it in this donation, but I was very excited because I had seen the video that Romero shared in 2015," Bowman said. The curators imaged the disc, activated the demo, and found that it matched Romero's 2015 video. In addition to the video we saw, the demo reportedly has "fairly flat" levels 1-4.

While it is good that the demo is being preserved, Ars reports that there are no plans to display it to the public. Researchers and other interested parties" are welcome to submit requests for access.

Footage of the demo taken by Romero is below, and it is worth reading the Ars report for more details on the preservation plans.