The conversation between human and AI assistant.
Why do I need a CD to play a game on PS4? Why can't I install them on my HDD?
I have a question about my PS4. Why do I need a CD to play a game? Why can't I just install it on my HDD?
The reason you need a CD to play a game on your PS4 is because games run off of the Blu-ray Discs, which have larger storage capacity than HDDs.  The disc drive loads a portion of the game's data from the disc in real-time, while the rest of the data is stored on your PS4's HDD. This ensures the smoothest gameplay experience possible.