Open VMS Operating System Concepts, Second Edition
A combination of general operating system theory and specific OpenVMS concepts makes this book interesting.
TABLE OF CONTENTS Open VMS Operating System Concepts, Second Edition
Chapter 2: The Process
Overview
The previous chapter used the term "program" to minimize the number of new terms being introduced. Most software engineers feel comfortable with "program." However, in the strict sense, the accurate term is "process." In this book the process is the smallest software unit managed by the operating system and since it is the prime unit with which the operating system must deal, the user should attain a good understanding of the concept as soon as possible.
2.1 THE PROCESSING AND OPERATING SYSTEM
A software engineer writes a program to perform a function; then the program is complied, linked, and executed. Once the program is executing, it becomes part of the user's process. The user's process is represented in the operating system by a collection of data elements. These include the user's program and where it is located, accounting information, privilege flags, information about current files, performance statistics, and so forth. This chapter outlines and develops the Open VMS process database. It also follows a process' lifetime shown in Figure 2.1 beginning with process creation at the user login time and continuing with the activation of DCL (Digital Command Language), which is the code that prompts, reads, and executes commands from the terminal. DCL works in conjunction with a subroutine called image activation. An image is a user program that executes as part of the process. ("Program" and "image" are used synonymously for the rest of the book.) Many images are activated, the most familiar being the activation...
Copyright Butterworth-Heinemann 1997 under license agreement with Books24x7
