Operating System

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Module 4

• Operating System
• Fundamentals

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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\gt where C\
  represents the hard disk drive root directory,
  and 'gt' 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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