The Instruction Architecture Level (ISA)

In this section, we will show how a computer can be described in different ways and explain that this book is about computers from the point of view of their instruction sets and capabilities.

The term computer means different things to different people. To an engineer, a computer is a collection of circuits that perform a certain function; to a pilot, it’s a machine that flies an aircraft from one airport to another and can land it in thick fog.

Table 3.1 demonstrates the hierarchy of computer languages and structures. At the top you have the actual application for which the computer is used. At this level, the application may be a user-selected program (flight simulator), or it may be a program that runs on an embedded system (e.g., an ATM). Communication with that application is universal and independent of the actual computer on which the application runs.

Level ...