Ch. 4 Operating System Fundamentals

IT Essentials I v. 3
Module 4
Operating System Fundamentals
© 2004, Cisco Systems, Inc. All rights reserved.
Module 4
Operating System Fundamentals
4.1 – The Operating System
4.2 – Disk Operating System (DOS)
4.3 – Memory Management
The Operating System
Components of an Operating
• Operating Systems (OS)
are software programs that
control thousands of
operations, provide an
interface between the user
and the computer, and run
• An OS is designed to
control the operations of
programs such as web
browsers, word processors,
and e-mail programs.
Components of an Operating
Computers that handle
concurrent users and multiple
jobs are called "network
servers" or "servers“.
Servers have operating systems
installed called Network
Operating Systems (NOS).
There are three basic elements
that make up the major design
components of any operating
1. User interface
2. Kernel
3. File management system
Operating System Functions
• 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
hardware (The operating system
can either access the hardware
through the BIOS or through the
device drivers Figure 2)
• Programs written for the UNIX
operating system will not work on
a Windows-based system, and
vice versa.
Operating System Types - Basic
• The following terms are often
used when comparing operating
• A list of some of the most
popular operating systems:
Microsoft Windows 95, 98, ME
Microsoft Windows NT/2000/XP
The Macintosh OS
Disk Operating System (DOS)
What is DOS, and
Why Learn About it?
• Microsoft developed (DOS), in
1981. DOS was designed for
the IBM Personal Computer
• DOS is a collection of
programs and commands
used to control the overall
computer operation in a diskbased system
• Three sections make up DOS:
– Boot files
– File management files
– Utility files
What is DOS, and
Why Learn About it?
• DOS is useful as a troubleshooting aid when
Windows will not boot. It allows the hard drive to be
accessed without the GUI and provides the ability to
run troubleshooting or diagnostic programs.
– DOS is a command line operating system, it is not
– DOS can only run one program at a time.
– DOS can only run small programs and has memory
– DOS is an essential tool for IT professionals and is
used extensively for troubleshooting
The DOS File Structure
• A file is simply a block of
logically related data that is
given a single name and treated
as a single unit.
• Examples include programs,
documents, drawings and other
illustrations, sound files, etc.
• The common attributes for DOS
files include:
Hidden File
Read Only
Archive (backup) status
System File
The DOS File 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 the
drive, directory, and subdirectory in which the file is
• The first hard drive in most computer systems is
labeled “C”.
Overview of Basic DOS
• Basic commands are generally
internal and more advanced
commands are usually external.
• 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.
• A switch is added to the
command by adding a space, a
forward-slash (/), and a single
Creating a DOS Boot Disk
• A DOS boot disk is a great
tool to use to troubleshoot
when the computer is not
booting properly.
• A DOS boot disk is just a
floppy disk with three
necessary system files on it:
Booting the System with a DOS Disk
• A DOS boot disk is used to boot a
computer to the DOS Prompt
• Insert a bootable disk in the floppy
disk drive, and turn on the
• The BIOS will execute the
bootstrap program to move the
master boot record into RAM and
then begin loading the operating
• If the system performs a standard
DOS boot up, it should print the
Date and Time prompts on the
monitor screen, followed by the
command line prompt (A:\).
DOS Configuration Files
• In the MS-DOS operating system, there are two
special configuration files, called CONFIG.SYS and
• As the system moves through the steps in the boot
procedure, the BIOS first checks in the root directory
of the boot disk for the presence of the CONFIG.SYS
• Next, it searches for the COMMAND.COM
interpreter, and finally looks in the root directory again
for the AUTOEXEC.BAT file.
• Both the AUTOEXEC.BAT and CONFIG.SYS files
can play significant roles in optimizing the system
Editing System Configuration
• SYSEDIT is a standard text
editor used to edit system
configuration files such as
Config.sys and Autoexec.bat.
• This utility can be used to edit
the set of Windows
initialization files generally
referred to as INI files.
• INI files are basically text files
that users can edit with a
standard text editor utility such
Memory Management
Memory Types
• The operating system that runs the computer
uses physical memory (RAM), also known as
system memory, and virtual memory.
• The four categories of system memory in the
operating system include:
Extended memory
Memory Types
• Conventional memory
includes all memory
addresses between 0 and
• It is also known as base
memory. This is the area
where MS-DOS programs
normally run.
Memory Types
• Upper Memory/Expanded
Memory is also known as
Reserved Memory
• It includes memory
addresses that fall between
640KB and 1024KB (1MB).
• It follows conventional
memory and has a size of
Memory Types
• Extended Memory
is memory locations beyond
the 1 MB limit of the
• This area of memory is also
called Extended Memory
Specification (XMS).
• XMS is the primary memory
area used by Windows 9x.
Memory Types
• Once the XMS driver is
loaded, extended memory
becomes available to the
• When this happens, the first
64KB of extended memory
is called the High Memory
Area (HMA).
Memory Management Tools
• There are several tools that
can be used to manage and
optimize system memory.
– EMM386.EXE
Other Types of Memory
• Two examples are RAM drive and virtual memory:
• Virtual memory is used to describe memory that is
not what it appears to be. Hard disk drive space is
manipulated to seem like RAM.
• It is the basis of multitasking in Windows 9x. Without
virtual memory, it would be almost impossible to run
most of the software in use today.
Memory Conflicts: GPF
• Memory conflict can lead to a
condition called General
Protection Fault (GPF).
• A GPF (“blue screen of death”)
typically occurs 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
– Tries to interact with a failing
hardware driver
– Tries to have direct access to the
system hardware
Real Versus Protected
Mode Memory Addressing
• Real mode means that software can address
only 1,024 KB (1 MB) of RAM.
• Protected mode allows one program to fail
without bringing down the whole system.
What happens in one area of memory has no
effect on other programs