The Easy Guide
To
Computer
Operating Systems
By Larry Miller

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Table of Contents
T
able of Contents

....................................................................................................... . . . . . . . . . .2
IN
TRODUCTION

....................................................................................... . . . . . . . . . . . . . . . . . . . . . . . .3
W
HAT IS AN OPERATING SYSTEM?

............................................................... . . . . . . . . . . . . .5
H
ISTORY OF OPERATING SYSTEMS

................................................. . . . . . . . . . . . . . . . . . . . . . . . . . .9
W
HAT AN OPERATING SYSTEM DOES

........................................................... . . . . . . . . . .13

P
rocess Management

.......................................................................... . . . . . . . . . . . . . . . . . . . . . . . . . . .13

M
emory Management

......................................................................................... . . . . . . . . . . .19

D
isk and File Systems

................................................................................................ . . . .23

N
etworking

......................................................................................... . . . . . . . . . . . . . . . . . . . . . . . . . . .24

S
ecurity

...................................................................................................... . . . . . . . . . . . . . . . . . . . .25

Int
ernal Security

...................................................................................................... . . . . . . .27

E
xternal Security

........................................................................................................ . . . .28

G
raphical User Interfaces

.................................................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . .29

D
evice Drivers

.......................................................................................... . . . . . . . . . . . . . . . . . . . . .29

A
pplication Interface

.......................................................................... . . . . . . . . . . . . . . . . . . . . . . . . . . .31

M
ICROSOFT WINDOWS

...................................................................................... . . . . . . . . . .34

M
AC OS

..................................................................................................... . . . . . . . . . . . . . . . . . . . . . . .45

U
NIX


..................................................................................................................................

51

L
INUX

.............................................................................................................. . . . . . . . . . . . . . . . . .54

G
NU

......................................................................................................................... . . . . . . . . . .57

O
THER OPERATING SYSTEMS

..................................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

IN
STALLING AN OPERATING SYSTEM

...................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62

D
EFINING THE PROCESSES

............................................................................... . . . . . . . . . .66

Ca
che


..............................................................................................................................

66

V
irtual Memory

.................................................................................. . . . . . . . . . . . . . . . . . . . . . . . . . . .74

2

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System Resources



........................................................................................................................................

76

RAM



........................................................................................................................................

77

Computer Memory



........................................................................................................................................

84

CO

NCLUSION

........................................................................................................... . . . . . . .91

INTRODUCTION
Our body couldn't function without our brains. The brain tells
the various pieces of our body how to work and how to interact.
Without a brain, we wouldn't be able to do anything at all.
An operating system is kind of like the brain of a computer. You
have a bunch of hardware like the CPU tower, the monitor, and the
keyboard, but without a CPU, they can't do anything but power up and
turn on. The operating system organizes files and lets the hardware
know what it should do.
In the early days of computers, there was just one operating
system. As computers progressed, the OS turned into MS-DOS, but
computers really weren't capable of doing much without software.
Then Bill Gates came along.
With the founding of Microsoft, the computer operating system
came into its own and brought computers to new levels of functioning
and technology. Although the brand names of operating systems are
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few, they do perform different tasks depending on the requirements of
the computer user.
While the dominant OS today would be Microsoft Windows, there
are other types of operating systems that offer different features.
Those would include Linux, UNIX, and OS X.
In our technological age, there are operating systems in more
than just computers. Many of the sophisticated new cell phones have
their own operating systems, and wireless access points have their
own OS to provide wireless internet to customers. In fact, the
computer in a cell phone today is more powerful than a computer was
twenty years ago.
As you can see, the operating system technology has evolved
and is continuing to evolve. It seems like Microsoft is always coming
out with a new and better operating system which leads people to
wonder whether or not the system they are currently using is really
the best one.
It can be confusing. But it doesn't have to be. In the pages of
this book, we'll explore operating system in depth. You'll learn about
what they do, how they work, and what needs specific systems can
meet. Ultimately, the choice is a matter of preference, but it helps to
be informed on what you are really getting when choosing an OS.
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WHAT IS AN OPERATING SYSTEM?
An operating system - commonly referred to as an OS - is a set
of computer programs that manage the hardware and software
resources of a computer. The OS processes electronic devices with a
rational response to commands that are approved by the system.
At the foundation of all system software, an operating system
performs basic tasks like controlling and allocating memory,
prioritizing system requests, controlling input and output devices,
facilitating the network, and managing files. The OS can also provide
a graphical user interface for higher functions. Essentially, the OS
forms a platform for other system software as well as application
software.
The operating system is the most important program that runs
on a computer. Without an operating system, your computer would
not work. It would not be able to process requests for print, simple
calculations, or any other function. It is really the brain that runs the
equipment.
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For larger system, the OS has great responsibilities than with a
PC. In larger systems, the operating system is kind of like a traffic
cop. It makes sure that different users and programs running at the
same time on different systems don't interfere with each other. It also
acts as a security guard making sure that unauthorized users are not
able to access the system.
There are four classifications of a computer operating system.
They are:
* Multi-User: Allows two or more users to run programs at the
same time. Some operating systems permit hundreds or even
thousands of concurrent users
* Multi-Processing: Supports running a program on more than
one CPU
* Multi-Tasking: Allows more than one program to run
concurrently
* Multi-Threading: Allows different parts of a single program to
run concurrently
* Real Time: Responds to input instantly. General-purpose
operating systems, such as DOS and UNIX, are not real-time.
Operating systems provide a software platform on top of which
other programs, called application programs, can run. The application
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programs must be written to run on top of a particular operating
system.
Your choice of operating system, therefore, determines to a
great extent the applications you can run. For PCs, the most popular
operating systems are DOS, OS/2, and Windows, but others are
available, such as Linux.
In any device that has an operating system, there's usually a
way to make changes to how the device works. This is far from a
happy accident; one of the reasons operating systems are made out of
portable code rather than permanent physical circuits is so that they
can be changed or modified without having to scrap the whole device.
For a desktop computer user, this means you can add a new
security update, system patch, new application or often even a new
operating system entirely rather than junk your computer and start
again with a new one when you need to make a change.
As long as you understand how an operating system works and
know how to get at it, you can in many cases change some of the
ways it behaves. And, it's as true of your cell phone as it is of your
computer.
So, essentially, when you turn on your computer, the first
program is a set of instructions kept in the computer's read only
memory. These instructions examine the system hardware to make
sure everything is functioning properly. This power-on self test check
the CPU, the memory, and the basic input/output systems (BIOS) for
errors and stores the result in a special memory location.
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Once the test has successfully completed, the software loaded in
ROM (sometimes called the BIOS or firmware) will begin to activate
the computer's disk drives. In most modern computers, when the
computer activates the hard disk drive, it finds the first piece of the
operating system: the bootstrap loader.
The bootstrap loader is a small program that has a single
function: It loads the operating system into memory and allows it to
begin operation. In the most basic form, the bootstrap loader sets up
the small driver programs that interface with and control the various
hardware subsystems of the computer.
It sets up the divisions of memory that hold the operating
system, user information and applications. It establishes the data
structures that will hold the myriad signals, flags and semaphores that
are used to communicate within and between the subsystems and
applications of the computer. Then it turns control of the computer
over to the operating system.
It might be helpful for you to know the history of operating
systems.
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HISTORY OF OPERATING SYSTEMS
The earliest of computers didn't have an operating system. By
the early 1960's, commercial computer vendors were supplying quite
extensive tools for streamlining the development, scheduling and
execution of jobs on batch processing systems.
Through the 1960's, several concepts were developed which
drove the development of operating systems. The IBM System 360
produced a family of mainframe computer that served consumers with
differing capacities and prices. A single operating system was planned
for these computers rather than developing generic programs for
every individual model.
This concept of a single OS that will fit an entire product line was
crucial for the success of System 360. In fact, IBM's current
mainframe operating systems are distant relatives of this original
system. The advantage to this is that applications written for the OS
360 can still be run on modern machines.
The OS 360 system also contained another important advance
affecting today's computers: the development of a hard disk
permanent storage device which IBM called DASD.
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A second key development was the concept of time sharing.
Time sharing involves sharing the resources of expensive computers
among multiple computer users interacting in real time with the
system. What that essentially means is that all of the users have the
illusion of exclusive access to the machine. The most famous of time
sharing system was called Multics.
Multics served as an inspiration to a number of operating
systems developed in the 1970's. Most notably was the Unix system.
Another commercially popular mini-computer operating system was
VMS.
The first microcomputers did not have the capacity or need for
the elaborate operating systems that had originally been developed for
mainframes and minis. Smaller operating systems were developed
and often loaded from ROM and known as Monitors.
One notable early disk-based OS was CP/M which was supported
on many early micro-computers and was largely cloned when MS-DOS
was created. MS-DOS became wildly popular as the operating system
chosen for the IBM PC.
The successive operating systems that came from MS-DOS made
Microsoft one of the most profitable companies in the world with the
development of Windows. The only other alternative throughout the
1980's was Mac OS which was tied intimately to the Apple McIntosh
computer.
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