How do patches work for disc-based games (i.e. on Xbox 360)?

Question

Games on the current and next generation of consoles are required to be installed to the hard drive, and cannot be run straight off the disc. On the Xbox 360 (not sure about the PS3, never owned one), installations are normally optional, with the exception of certain games later in the console’s lifetime due to the constraints of a 8.5GB DVD-DL.

This begs the question, how do devs patch disc-based games on the 360? Since you can’t change the content of what’s on the disc, and installs are optional. How does the game know not to use a file or a line of code, or whatever that’s on the disc, but instead use content from the patch that’s installed to the hard drive?

In: Technology

Answer 1

Installs were optional, but the game’s code had to be pulled into memory in order to execute. Once loaded into memory, the console could apply the stored patch to the in-memory code before it’s executed.