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Operating System

Fundamentals

Module 4

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Operating Systems

• Operating Systems (OS) are software programs that control

thousands of operations, provide an interface between the

user and the computer, and run applications.

• An OS is designed to control the operations of programs such

as Web browsers, word processors, and e-mail programs.

• Computers that are capable of handling concurrent users and

multiple jobs are often called "network servers" or simply

"servers." Servers have operating systems installed called

Network Operating Systems (NOS).

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Operating Systems

• There are three basic elements that make up the major design components of any operating system. These components are:

– User interface – A user interacts with the computer's OS through the user interface. Simply put, the user interface is the part of the operating system that a person can use to issue commands.

– Kernel – This is the core of the OS. The kernel is responsible for loading and running programs (processes) and for managing input and output.

– File management system – The file management system is what the OS uses to organize and manage files. Most operating systems use a hierarchical file system in which files are organized into directories under a tree structure. The beginning of the directory system is referred to as the root directory.

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Operating Systems Functions

• Regardless of the size or complexity of the computer or its

operating system, all operating systems perform the same

basic functions:

• File and folder management

• Management of applications

• Support for built-in utility programs

• Access control to computer's hardware

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Operating Systems Functions

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Operating Systems Types - Basic Terminology

• Multi-user – Two or more users running programs and sharing

peripheral devices, such as a printer, at the same time.

• Multi-tasking – A computer's capability to run multiple

applications at the same time.

• Multi-processing – Allows a computer to have two or more CPUs

(Central Processing Unit) that programs share.

• Multi-threading – The capability of a program to be broken into

smaller parts that can be loaded as needed by the OS. Multi-

threading allows individual programs to be multi-tasked.

Today, almost all operating systems are multi-user, multi-tasking,

and support multi-threading.

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Popular Operating Systems

• Microsoft Windows 95, 98, ME – Windows is one of the

most popular operating systems today. Windows is designed

to run on PCs and to use an Intel-compatible CPU. Windows

9x systems are designed to be run and maintained by a single

user.

• Microsoft Windows NT/2000/XP –Windows NT, 2000 and

XP are operating systems that were designed to support

multiple (concurrent) users and to run applications

simultaneously. Both Windows NT and Windows 2000/XP

have incorporated many networking features.

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Popular Operating Systems

• The Macintosh OS – The first Macintosh computers became

available in January of 1984 and were designed to be very

user-friendly compared to the existing DOS computers. The

latest release of the Macintosh Operating System, OS X, is

highly functional and is based on Unix as its core technology.

• UNIX – UNIX, which has been around since the late 1960s, is

one of the oldest operating systems. UNIX has always been

popular with computer professionals whose responsibility is to

run and maintain computer networks. There are many

different versions of UNIX today. One of the most recent is the

extremely popular Linux.

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Disk Operating Systems

• Microsoft developed the Disk Operating System (DOS), also

called MS-DOS, in 1981.

• DOS was designed then, for the IBM Personal Computer.

• Windows 98 and Windows 2000 both support DOS

commands in order to address compatibility issues related

with older applications.

• Simply put, DOS is a collection of programs and commands

used to control the overall computer operation in a disk-based

system.

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Basic Elements of DOS

• The following are some of the basic things to remember when

working with DOS.

• DOS is a command line operating system; it is not user-

friendly. The best way to learn DOS is to use it.

• DOS can only run one program at a time. It is not

multitasking.

• DOS can only run small programs and has memory

limitations.

• DOS is an essential tool for IT professionals and is used

extensively for troubleshooting.

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DOS File Structure

• Programs and data are stored the same way a document

would be filed in a folder in a file cabinet.

• In DOS, they are called files and are grouped together in

directories.

• Directories are much like the folders in the file cabinet.

• Directories can be nested inside other directories, just like a

folder placed inside another folder. Nested directories are

referred to as subdirectories.

• Directories became known as folders in the Windows OS.

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DOS Files

• A file is simply a block of logically related data, given a single

name, and treated as a single unit, such as programs,

documents, drawings and other illustrations, sound files, and

so on. Files are referred to by filenames.

• In DOS, filenames can be up to 8 characters with an

extension of 3 characters. (8 + 3)

• The extension is separated from the main portion of the

filename by a period and it identifies what type of file it is.

• Example: mynotes.txt

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DOS File Attributes

• In DOS, all files have attributes, which are a set of parameters

that describe a file. The common attributes for DOS files

include:

• Hidden File – The user will not see this type of file with any

kind of normal file search in a DOS environment.

• Read Only – The user can open and read this type of file

but cannot write or modify the file in any way 

• Archive (backup) status

• System File – A file needed by the DOS operating system

for a successful bootup

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DOS Directory Structure

• Hard drives organize the disk into directories and

subdirectories.

• The main directory is known as the root directory.

• All other directories, if they exist, then radiate (branch out)

from the root directory, similar to the branches of a tree.

• Locating any given file requires knowledge of three things: the

drive, directory and subdirectory in which the file is found.

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DOS Directory Structure

• In MS-DOS, the format for specifying the path to a file is as

follows:

• C:\directory name\subdirectory name\filename

• The first back slash indicates the root directory, which is

present on all DOS disks

• The back slash (\) after each item signifies the presence of

a directory or subdirectory

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Basic DOS Commands

• In DOS, the main user interface is the command line.

• The command line is the space immediately following the

DOS prompt, C:\> where C:\ represents the hard disk drive

root directory, and '>' is known as the prompt.

• All the DOS commands are typed to the right of the prompt

and executed by pressing the return (ENTER) key on the

keyboard.

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Basic DOS Commands

Scandisk checks the integrity of the computer hard disk or floppy disk.

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DOS Boot Disk

• To troubleshoot the problem, an alternate way of starting the

system is needed. A DOS boot disk is a great tool to use to

perform this task.

• One of its most useful functions is in booting a newly

assembled computer to install the operating system.

• A DOS boot disk is just a floppy disk with the three necessary

system files on it, including:

• COMMAND.COM

• IO.SYS

• MSDOS.SYS

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Booting a System with a DOS Boot Disk

• A DOS boot disk is used to boot a computer to the DOS

Prompt.

• On the very first section of a DOS disk is a section called the

boot sector.

• The boot sector contains information about how the disk is

organized.

• Sometimes, it contains a small optional master boot record

that can access a larger, more powerful bootstrap loader

program, which is located in the root directory.

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CONFIG.SYS

• The config.sys in most Windows 9x will be empty (plain text

file) waiting for any changes that the user might want to add to

the system.

• In the migration from DOS to Windows 9x, most of the values

formerly located in this file have been moved to IO.SYS.

• If you want to override values in IO.SYS, enter the appropriate

statements in Config.sys, including the values.

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AUTOEXEC.BAT

• This file contains a batch of DOS commands that will

automatically be carried out when DOS is loaded into the

system.

• Examples of commands normally located in the Autoexec.bat

file include:

• DATE – Causes DOS to prompt user for the date

• TIME – Causes DOS to prompt the user for the date and

time

• DOSKEY – loads the DOSKEY

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Booting From a DOS Disk

When booting from a DOS boot disk, the boot process occurs in

the following order:

• BIOS

• Bootstrap

• IO.SYS

• MSDOS.SYS

• CONFIG.SYS (if present)

• COMMAND.COM

• AUTOEXEC.BAT (if present)

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Physical Memory Allocation

• Four categories of system memory in the operating system

includes conventional, upper/expanded, high, and extended

memory.

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Physical Memory Allocation

• Conventional memory includes all memory addresses between 0

and 640KB. It is also known as base memory.

• Upper memory/Expanded memory includes memory addresses

that fall between 640KB and 1024KB (1MB). Expanded Memory.

This is memory that can be accessed in pages (16KB chunks)

from a 64KB page frame, established in unused Upper Memory

Blocks. EMM386.EXE controls expanded memory.

• Extended memory includes memory addresses above 1024KB. It

is controlled be HIMEM.SYS

• The first 64KB of extended memory is called the High Memory

Area (HMA). When activated, Windows 9x runs here.

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Virtual Memory

• Also known as swap file or page file is used to describe

memory that is not what it appears to be.

• Hard disk drive space is manipulated to seem like RAM.

• The combination of virtual memory and actual installed

physical memory, gives the appearance of more memory than

is actually installed on the system.

• Virtual memory is the basis of multitasking in Windows 9x.

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Virtual Memory

• Memory conflict can lead to a condition called General

Protection Fault (GPF). A GPF will typically occur when an

application attempts to violate the system integrity by one of

the following ways:

– Tries to use a memory address or space owned by another

application

– Tries to interact with a failing hardware driver

– Tries to have direct access to the system hardware

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