Concepts and Semantics of Programming Languages 1

1From Hardware to Software

This first chapter provides a brief overview of the components found in all computers, from mainframes to the processing chips in tablets, smartphones and smart objects via desktop or laptop computers. Building on this hardware-centric presentation, we shall then give a more abstract description of the actions carried out by computers, leading to a uniform definition of the terms “program” and “execution”, above and beyond the various characteristics of so-called electronic devices.

1.1. Computers: a low-level view

Computer science is the science of rational processing of information by computers. Computers have the capacity to carry out a variety of processes, depending on the instructions given to them. Each item of information is an element of knowledge that may be transmitted using a signal and encoded using a sequence of symbols in conjunction with a set of rules used to decode them, i.e. to reconstruct the signal from the sequence of symbols. Computers use binary encoding, involving two symbols; these may be referred to as “true”/”false”, “0”/”1” or “high”/”low”; these terms are interchangeable, and all represent the two stable states of the electrical potential of digital electronic circuits.

1.1.1. Information processing

Schematically, a computer is made up of three families of components as follows:

• – memories: store data (information) and executable code (the so-called von Neumann architecture);
• – one or more microprocessors, known as CPUs ...