So I understand the concept for movies that are on DVD or Blu-Ray, as the disc spins the encoded data of the image that is on the disc is more or less read by the disc-player and displayed on the screen. But movies are linear and the disc just has to spin with the laser moving in a little every rotation and voila, movie I suppose. But with video games how are all the moving parts of the game, and my inputs and whatnot, read by the system off the back of a disc? Wouldn’t various parts of the code be in differing places on the disc? How does it jump back and forth between disc locations so quickly? How much of the game I’m playing is actually a result of the information on the disc, and how much comes from the part that I have to download whenever I put in a new game’s disc? Is the disc essentially just an installer wizard that allows me to download the actual game?
In: Technology
The very crude overview of things, assuming no internet connection, is that the game reads from disc the “core engine”, and puts it onto memory(RAM) of the console. This engine stays loaded in the RAM constantly.
In older games, when you started playing the game, your game engine would then instruct to read specific parts of the disc required for the first level. All these would be put into RAM as well, and for the most part disc was unnecessary for a while now. But while disc was being accessed, you’d be shown loading screen
Then, you would complete the level, so the level-specific things for the first level, and check the disc again for things required for the second level. Again, loading screen.
Lately many games have tried to do away with loading screens and they try to constantly access the disc so that they keep loading and unloading things from RAM without you noticing. This is called “streaming”. Anyway, the core concept still would remain the same, there is core engine loaded which knows what to load and when, and when to discard things. If for whatever reason you have to wait for the disc, optimal situation is you’re shown loading screen or something similar(some games actually include long bland hallways or such to avoid having to have loading screens, with the idea that player walking through the bland hallway allows time for the game to actually load the next area properly). Worst case scenario is that the game basically freezes on you for a while, stuttering a lot.
I haven’t really tested this lately but at least with PSX, the original Playstation, games, in games with strong level-to-level progression, you could safely remove the game disc in the middle of the level and usually the level would play completely normally. It would only crash after you tried to move to another level when it tried to get assets for that next level and realize everything is missing.
Disc is just a container for the data of the game. To actually use it, like any computer, you need to first get it into memory, that is, RAM. All the data computers or their variants process will always go to RAM first and only after that you can do something with them. With games, when game is starting up, it will load up the things required for core functionality of the game, and it will then more or less often use disc. If you see loading screens, that’s the main avenue where disc access(or hard drive access) happens. Nowdays though many of the times loading screens are hidden in clever ways. For example, while the next level is being loaded, you can show player a cutscene. You can make them wait for something to happen, or walk a long corridor. Forcing perspective of the player away from the area that’s being loaded works wonders as well. And the most seamless experience is streaming assets design, where game constantly keeps loading things that you might be needing soon, and unloading things that don’t seem likely to be used soon.
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