In this chapter we look at manual computation and ask how it can be automated. We shall identify the main components of an automatic computing machine and decide how to replicate their function using digital components. This leads to the design of a machine called Simple Machine. We develop the design of Simple Machine by adding a few data storage registers and including logic to control three flags. These flags allow the machine to perform conditional branch instructions. The resulting computer is called G80. We shall add further improvements to G80 as the need arises in subsequent chapters.
5.1 A manual computing system
Consider a manual computing system of the sort that was common until the 1960s, Figure 5.1. Here the computer ...