Microprocessor 1

3Computation Model and Architecture: Illustration with the von Neumann Approach

A user working today in front of his or her microcomputer workstation hardly suspects that he or she is in front of a machine whose operation is governed by principles described by the mathematician John von Neumann in the 1940s¹ (Ceruzzi 2000). This remains the case when modern terms such as “superscalar architectures” and “multicore” or accelerating mechanisms like the pipeline, concepts discussed in the forthcoming Volume 2, are mentioned. Before studying the functioning of the microprocessor, we need to clarify the theoretical concepts of the computational model and computer architecture. The so-called von Neumann approach, which still governs the functioning of computers internally despite all the progress made since it was developed, is described by presenting the basic execution diagram for an instruction. This architecture has given rise to variations, which are also presented. Finally, the programmer needs an abstraction of the machine in order to simplify his or her work, which is called the “Instruction Set Architecture” (ISA). It is described before the basic definitions for this book, which complete this chapter.

NOTE.– In this book, the term CU for “Central Unit” (or CPU for Central Processing Unit) is taken from the original word, that is, the unit which performs the computations, and not from the microcomputer itself. It most often describes the microprocessor also referred to as ...