A lot of the time, the game itself is not entirely stored on the disk (or maybe not even at all). When you first put the disk into your console, it goes to the internet and downloads a lot of the game’s content from a server somewhere and installs it on your console’s hard drive.
This disk is mostly just a physical representation of the license that you purchased for the game; it is not the game itself. Most modern games can be played without a disk or purchased 100% digitally.
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