Friday Flashback: Screencast 90s style

While digitizing some old home movies from VHS-C magnetic tapes, I came across a 5 minute screencast that I created sometime in the mid 1990's. The term "screencast" dates from 2004. While I am certainly not the first person in the world to produce one, I did do it about 10 years before the name was coined. The program¹ used to generate these images was written about 10 years earlier still.

Three segments, edited from the one recorded screencast, are presented here. The first one (57 seconds) describes a particular one dimensional cellular automaton, which generates a fractal pattern over time.

The next one (38 seconds) describes a different one dimensional cellular automaton, which demonstrates what is called a "glider". Over time a configuration of cells moves, in this case to the right. A mirror image of this configuration would move to the left.

The final segment (90 seconds) uses the same cellular automaton rules² as the previous one, and shows what is called a "glider gun". As time progresses, this configuration of cells emits gliders regularly, first one moving to the right, then another moving to the left, and so on. In a wrap-around world, like the one I used in this Apple ][ program, the glider moving to the right soon meets up with the next one moving to the left and the two annihilate each other.

Creating a screencast with an Apple ][ was not difficult, and did not require any software, since this personal computer used an ordinary television set as its monitor. So it was a simple matter to take the output of the TV, using an RCA video cable, and connecting it to the video-in of a camcorder. The voice over was captured by the built-in microphone of the camcorder, as I operated the keyboard and watched the screen.

1. I wrote the program myself, in 6502 machine language, in the mid 1980's. Unfortunately, this program no longer exists, being a victim of digital decay.
2. The cellular automata rules come from a series of articles in Scientific American written by Stephen Wolfram. The subscription to Scientific American was initially a gift from a former professor (who was also influential in my decision to major in Computer Science), Dr. Alan C. Ashton.