Radiohead has never shied away from arty and elaborate "special edition" versions of its albums, which normally ship to fans with unique artwork and limited vinyl. But Tuesday's collector's item release of the OK Computer 20th anniversary edition, priced at a whopping $130/£100, shipped with that most hipster of audio formats included: a C90 audio cassette.

And if you're wondering whether Radiohead's bizarre, technology-theorizing landmark album would pack something computer-related into that cassette tape, you might want to dig up your old Sinclair ZX Spectrum cassette drive.

Radiohead's 78-minute cassette was distributed on Tuesday as a digital download to anyone who pre-ordered the box set (which also includes three vinyl records and three full books of art, sketches, and lyrics from the recording session). The cassette, packed full of rare demos and odd audio experiments, ends with roughly two minutes of computer tones.

At least one keen fan loaded this into a ZX Spectrum emulator (after processing the audio with a 3.5kHz low-pass filter). And the result is roughly 30 lines of code, with its functioning parts printing out a basic text greeting that lists the band members' names alongside a note: "19th December 1996, with all our love." (It's unclear whether that is the date that the members coded a ZX-specific program, or whether it signifies the final day of the album's recording sessions.) The greeting is followed by a minutes-long blast of randomly generated colors and beeps. The code's first 10 or so lines are commented out with a hidden message that reads, "congratulations....you've found the secret message syd lives hmmmm. We should get out more."

This message is particularly keen, because it may very well reference Syd Barrett, who got the boot from the band Pink Floyd when he began pushing experimental and psychedelic sounds (along with many other issues). OK Computer saw Radiohead push away from its own "traditional rock" sound and popularity with more synthesizers and textures. This aesthetic remained a band keystone for the rest of its career to date.

For decades, musicians have used musical releases to sneak Commodore and Sinclair computer code to fans. Perhaps the earliest example of the practice came in 1983 from British new-wave rocker Chris Sievey, who snuck a bonafide animated music video to his single "Camouflage" on its single's B-side. Early 2000s computer-music artist Paul Slocum packed his own music generating Commodore program onto the end of his band Tree Wave's debut EP. Slocum also pioneered a clever use of a dot matrix printer as a percussive instrument, and he coded a clone of Atari's Head-On that generated music as he played the game at concerts.

Now read our series of stories on forgotten audio formats...