Just to add some more details to what to3m said. The ST's screen address did have to be on a 256 byte boundary. With 160 bytes per scanline you could scroll 8

Just to add some more details to what to3m said. The ST's screen address did have to be on a 256 byte boundary. With 160 bytes per scanline you could scroll 8 scanline vertically by changing the screen address. People did work out a methods of scrolling the screen with finer control. Sync scrolling [1] used overscan techniques. ST screens had a border around the image, not filling the whole screen. Methods were developed to the bottom, right, left and top borders [2]. By combining left and right border removal different offsets could be generated to position the screen on any 16bit/pixel boundary [3]. [1] http://www.atari-forum.com/viewtopic.php?f=1&t=4357&sid=8a77efcf7c22a8117efeec8372136658 http://www.atari-forum.com/viewtopic.php?f=1&t=4357&sid=8a77... [2] http://aldabase.com/atari-st-fullscreen-demos-history/ http://aldabase.com/atari-st-fullscreen-demos-history/ [3] https://blog.troed.se/2015/12/23/overscan-and-sync-scrolling/ https://blog.troed.se/2015/12/23/overscan-and-sync-scrolling...