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Jan 23, 2019

Think OS

A Brief Introduction to Operating Systems

by Allen B. Downey

Download this book in PDF and HTML from

Copyright 2014 Allen B. Downey.

License: Creative Commons Attribution-NonCommercial 3.0 Unported License.


In many computer science programs, Operating Systems is an advanced topic. By the time students take it, they usually know how to program in C, and they have probably taken a class in Computer Architecture. Usually the goal of the class is to expose students to the design and implementation of operating systems, with the implied assumption that some of them will do research in this area, or write part of an OS.

This book is intended for a different audience, and it has different goals. I developed it for a class at Olin College called Software Systems.

Most students taking this class learned to program in Python, so one of the goals is to help them learn C. For that part of the class, I use Griffiths and Griffiths, Head First C, from O'Reilly Media. This book is meant to complement that one.

Few of my students will ever write an operating system, but many of them will write low-level applications in C, and some of them will work on embedded systems. My class includes material from operating systems, networks, databases, and embedded systems, but it emphasizes the topics programmers need to know.

This book does not assume that you have studied Computer Architecture. As we go along, I will explain what we need.

If this book is successful, it should give you a better understanding of what is happening when programs run, and what you can do to make them run better and faster.

Chapter 1 explains some of the differences between compiled and interpreted languages, with some insight into how compilers work. Recommended reading: Head First C Chapter 1.

Chapter 2 explains how the operating system uses processes to protect running programs from interfering with each other.

Chapter 3 explains virtual memory and address translation. Recommended reading: Head First C Chapter 2.

Chapter 4 is about file systems and data streams. Recommended reading: Head First C Chapter 3.

Chapter 5 describes how numbers, letters, and other values are encoded, and presents the bitwise operators.

Chapter 6 explains how to use dynamic memory management, and how it works. Recommended reading: Head First C Chapter 6.

Chapter 7 is about caching and the memory hierarchy.

Chapter 8 is about multitasking and scheduling.

Chapter 9 will be about threads.

Chapter 10 will be about synchronization with POSIX mutexes and condition variables.

A note on this draft

The current version of this book is an early draft. While I am working on the text, I have not yet included the figures. So there are a few places where, I'm sure, the explanation will be greatly improved when the figures are ready.


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