Radiohead's 'OK Computer' was one of the seminal albums of the 90s, but the band has hidden some even older ephemera on 'OKNOTOK,' a commemorative special edition release of OK Computer in honor of the album's 20th anniversary. An astute and dedicated fan has discovered that a strange high-pitched noise at the end of a demo tape actually translates into a program for the ZX Spectrum, a British computer from the 80s.
Included in OKNOTOK along with the vinyl is a classic C90 cassette tape with over an hour of rare demos, and the ZX Spectrum audio file is tagged on the end of that cassette. In other words, to find the Easter egg, fans would need a cassette player, which is a rare enough piece of technology already. Then, by equalizing the screeching audio, intrepid fans were able to match it up with the outdated computer's coding language, resulting in an equally odd series of images and bleeps as the output program.