THE MANY-PARTS PROBLEM
A single part functioning by itself or a few parts connected to function as a very Simple circuit usually poses no problem as far as “system design" goes. The engineers who designed the parts, especially if the parts are of a universal digital logic family type such as TTL, have done their best to make sure their designs have adequate noise margins, are free of redundancy, are logically optimized, and are in general good designs. Unfortunately, most systems consist of more than a few parts. An average microcomputer can, in fact, consist of many hundreds of parts. At this level of system complexity, the integrate circuit designers at the factory are no longer responsible for overall system operation. It is up to the system designer to make it work and make it work well.