Two basic ways: Computed: NOT truly random. Way back in the late 70s, I had a BASIC program that used to output the very same set of 8-digit 'random' numbers

Two basic ways: Computed: NOT truly random. Way back in the late 70s, I had a BASIC program that used to output the very same set of 8-digit 'random' numbers every time the program was used. (Unless you did a special thing the first time, to obtain a random seed to generate a different sequence of pseudo-random numbers. IIRC, it was the number of machine cycles since the last time the floppy disk was accessed.) Hardware: Truly random: The machine counts machine cycles with a small maximum number before it overflows and restarts at zero. The machine looks at the time difference between things like key presses, or disk-spins, or something else that varies in time. No matter how good you are the variation in time between your key-presses is never the same at the very small time-flow level. That number is used as a seed to a pseudo-random generator.