I recall many IBM-PC games are bootable games. I inserted a floppy , resets the computer, and then it directly boots into the game. The disk must contain a boot sector and drivers and such.

As well, although I think in the Amiga this was more common, to buy games that were already prepared like this.

At least on my circle for doing the same with PC games, we built the floppies ourselves, then again, it could be a side effect that you could hardly buy any legal games in Portugal during those days, even regular shops would sell pirated games as originals.