You still use paper. Instead of writing the game in a general purpose programming language you write it using logic gates. You get abstraction and modularity by

You still use paper. Instead of writing the game in a general purpose programming language you write it using logic gates. You get abstraction and modularity by designing larger components (adders, flip-flops, timers, shift registers) on separate pieces of paper and then including them as named black boxes in a higher-level diagram. The good news for the Pong developers is that most of those larger components were already available off-the-shelf. Common families of these chips, such as the venerable 4000-series and 7400-series logic families, began to appear on the market in the mid-1960's. Edit just to add another bit of nuance. If it still seems like an extremely difficult task without much precedent, I think the lineage of these early arcade games can be traced back through their older arcade siblings: pinball machines. People had been building more and more sophisticated pinball machines over the decades since their inception in the early 1930s. For a look into pinball machines, some of their history, and an amazingly deep dive into the workings of a 1970's model, check out Alec's pinball series on Technology Connections [1]. [1] https://www.youtube.com/watch?v=ue-1JoJQaEg&list=PLv0jwu7G_DFVAUoqtVxFVIu2oZc2GGyDf&index=1 https://www.youtube.com/watch?v=ue-1JoJQaEg&list=PLv0jwu7G_D...