system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is a new video game sometimes "ready to play" when less than half the game is downloaded?
gpt
Some games are packaged in a way that gives you what you need to start the game first. 

The game is a bunch of separate files. There’s sound, music, levels, character models etc. if the game is set up for it, you can download the title screen and the first level, and start playing before the final boss is downloaded.