This document is a compilation of my notes for COE 628: Operating Systems at TMU. All information comes from my professor’s lectures, as well as the course textbook *Operating Systems: Internals and Design Principles *****by Stallings.

Adam Szava - 2tor.ca

W2023

Table of Contents

Chapter 3 Textbook Notes

3.1 What is a Process?

Summary of Chapters 1 and 2:

• A computer platform consists of a collection of hardware resources, such as the processor, main memory, I/O modules, timers, disk drives, and so on.
• It is inefficient for applications to be written directly for a given hardware platform.
  • Numerous applications can be developed for the same platform. Thus, it makes sense to develop common routines for accessing the computer’s resources.
  • The processor itself provides only limited support for multiprogramming. Software is needed to manage the sharing of the processor and other resources by multiple applications at the same time (which is what multiprogramming is).
  • When multiple applications are active at the same time, it is necessary to protect the data, I/O use, and other resource use of each application from the others.

Our goal is to manage the execution of applications such that:

• Resources are made available to multiple applications.
• The processor’s time is switched among multiple applications so all appear to be progressing.
• All devices are used efficiently.

The approach taken is to rely on a model in which the execution of an application corresponds to the existence of one or more processes.

<aside> ➕ A process (in this context) is an entity that consists of two essential elements:

• program code
• set of data associated with that code </aside>

At any given point in time, while the program is executing, this process can be uniquely characterized by a number of elements, including:

All this information is stored in a data structure called a process control block, created and managed by the OS. The point is that the PCB contains sufficient information to interrupt a running process, and later resume execution, as if the interrupt had not occurred. The PCB is the key tool which allows the OS to support multiple processes.

A process consists of program code, associated data, and a PCB. For a single-processor computer, at any given time, at most one process is actually executing and that process is in the running state.

3.2 Process States