There's no really separate video memory on the original Mac, just the 21kb buffer that's updated by software. When it needs to, the video circuitry grabs the bu

There's no really separate video memory on the original Mac, just the 21kb buffer that's updated by software. When it needs to, the video circuitry grabs the bus and reads the pixels it needs and outputs them. (There's probably some caching in the controller, but not a lot - a single screen line tops, I'd wager)