On the Atari 2600 in 1982, David Crane had a 4 KB cartridge for the code, the pictures and the whole world. One screen saved as a black-and-white picture (160 by 192 dots) would take 3,840 bytes, 94% of the cartridge. And rolling a random screen at every edge would change the jungle behind you.

So the screen you're on is one byte. Its 8 bits pick the trees, the middle of the screen and what's on the path. Run off the right edge and the byte shuffles: four of its bits decide a new bit, everything slides over, and the new bit goes in. Walk left and the same shuffle runs backwards, so every screen comes back exactly as you left it. Crane called it a polynomial counter; programmers call it a linear-feedback shift register. Starting from 196, it visits every number from 1 to 255 once and comes home. The one byte it never makes is 0. Crane said he picked the starting screen so the easy screens teach you the skills for the later ones.

The jungle screens in this film are our own simplified version, built in code from the game's own byte sequence. The dice that change the jungle behind you are our own demonstration.

Which game's hidden numbers should we cut open next?

Sources: David Crane, "Classic Game Postmortem: PITFALL!", GDC 2011. Pitfall! instruction manual, Activision, 1982. Thomas Jentzsch, commented disassembly of Pitfall! (v0.9, 2001). Atari, Stella Programmer's Guide, 1979. Further reading: Nick Montfort and Ian Bogost, Racing the Beam (2009).
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