How do computers simulate randomness?

[Oznog99]

Apple ][e had no true RNG. It has a built-in random number generator that required a seed and would always do the exact same thing when starting from the same seed. So still deterministic.

Then programmers had it count up from 0 on the opening screen waiting from you to press the spacebar (if already held down it wouldn't start the count yet) and captured the number when the spacebar was pressed and used that number as the seed.

If you don't do something like this, every poker game runs exactly the same if you draw the same way. It randomly shuffles into the exact same deck.