You have seen how to form single and dual playfields in which the
playfield in memory is the same size as the display window. This section
shows you how to define and use a playfield whose big picture in memory is
larger than the display window, how to define display windows that are
larger or smaller than the normal playfield size, and how to move the
display window in the big picture.

 when the big picture is larger than the display window 
 maximum display window size