Generating fractals on a 50 year old IBM 1401 mainframe

When tech tinkerer Ken Shirriff came across a working IBM 1401 computer at his local Computer History Museum (in Mountain View, CA), he decided to write a fractal program for it in assembly language. Because of course he did!


To run the program, first you hit the “Power On” button on the IBM 1401 console. Relays clunk for a moment to power up the system and then the computer is ready to go (unlike modern computers that take so long to boot). You put the cards into the card reader and hit the “Load” button. The cards fly through the reader at the remarkable speed of 800 cards per minute so the Mandelbrot program loads in just over a second. The console starts flickering as the program runs, and every few seconds the line printer hammers out another line of the fractal. After 12 minutes of execution, the fractal is done. (Interestingly enough, the very first picture of a Mandelbrot set was printed on a line printer in 1978.)

It’s pure, delicious geekery, and the excuse “because it’s there” fully applies.