The copper was widely used in the OS not just to change the entire colour palette half-way down the screen - it could change the display resolution half-way dow

The copper was widely used in the OS not just to change the entire colour palette half-way down the screen - it could change the display resolution half-way down the screen, along with other things such as the colour depth and memory location of the bitmap data. This allowed the OS to support having multiple "screens" with different resolutions, colour depths, and palettes, and you could drag the front one down to reveal the one behind it. It would also be used to support double-buffering for displaying smooth videos or other moving graphics - you'd have the two buffers, and the copper would change which one was being displayed while the scan was in the flyback period between frames.