size of an entire character. Most computers including the Atari 8-bits accomplish coarse scrolling as described above — common examples are viewing a long BASIC program listing or directory of files. Coarse scrolling implemented by bulk movement of data is often the only method of scrolling possible on most computers. However, ANTIC provides direct hardware support for vertical and horizontal, coarse and fine scrolling taking the concept of a "view port moving over data" from a metaphorical illusion to literal implementation. These ANTIC features deliver rapid, smooth, full screen movement requiring negligible CPU time and so free the CPU for other work. All ANTIC display modes, Text and Map modes, can exercise the hardware scrolling features. Vertical Coarse Scrolling Vertical coarse scrolling is the easiest feature to exercise. The first Text or Map Mode instruction in every Display List always includes the LMS instruction modifier specifying the start of screen memory. As it generates the display, ANTIC automatically increments its memory scan pointer from Mode line to Mode line to display memory contiguously. Therefore, a display can be "moved" by merely updating the initial LMS modifier's address; adding the number of bytes used for a line in the current Text or Map Mode shifts the screen contents up one line while subtracting the same amount moves the screen down. So, the display is actually a view port that is moved to look at a different areas of memory rather than moving the memory into a fixed screen map. Since ANTIC's memory scan counter cannot automatically increment over a 4K boundary the limit of vertical scrolling in this simple manner is up to 4K of movement. A full screen of Mode 2 text using approximately 1K can continuously scroll the height of four screens until reaching the 4K boundary. Likewise, a Mode 7 text display can scroll the height of 16 entire screens. Naturally, that trivial example is of limited usefulness. Many scrolling implementations scroll only part of the screen while other sections remain fixed. This problem is solved by the inherent capabilities of the ANTIC Display List. In this situation the Display List would add Mode instructions using LMS modifiers on the first mode line of the screen sections that should not move which effectively locks these parts of the display while the LMS modifier address for the scrolling section is updated. Further enhancement of this concept uses the LMS