Why is Metroid so Laggy? Part 1 - Loading Rooms and Running Out of Time - Behind the Code

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The #FamicomDiskSystem, which Metroid was first coded for, had an additional sound chip which Metroid used, so when it was ported to the NES sound processing had to be done in the frame time which lags more frames.
Also, Metroid loads rooms all at once as you move around the game, so when you cross the seams it lags! 😳