Going through the ROM code of 8 bit machines from 1980s would still be a tedious exercise. Much of the programming effort was spend on dealing with the limitati

Going through the ROM code of 8 bit machines from 1980s would still be a tedious exercise. Much of the programming effort was spend on dealing with the limitations of the hardware, rather than on accomplishing anything particularly interesting conceptually. It may be more effective to look at some simple system designed for teaching. For example, Oberon project from N. Wirth at ETH.(http://www.projectoberon.com/ http://www.projectoberon.com/)