you=the user :) Perform poke something, something and the bit is there. No need to call fancy update routines. I mean, this is still not a proof that all the video data is routed through the CPU, but if it was, wouldn't everything go blank whenever you run your asm program, just because it takes up 100% CPU time and CPU can't update the video? Video chips accessed the memory directly to grab the "screen area" and display it. Changes on screen were performed by changing that area. Only mode changes etc were performed by accessing the chips directly (though memory mapped SFRs too).