the development of the macintosh system software up to system 6 followed a fairly smooth progression with the addition of new features and relatively small changes and upgrades over time. major additions were fairly limited, notably adding color quickdraw in system 6. some perspective on the scope of the changes can be seen by examining the official system documentation, inside macintosh. this initially shipped in three volumes, adding another to describe the changes introduced with the mac plus, and another for the mac ii and mac se.