Intro To Computer by coooolone

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Intro To Computer Lecture No.07

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									  INTRODUCTION TO COMPUTER                                                  LECTURE 07



  WHAT IS AN OPERATING SYSTEM?
         An operating system (OS) is a software program, but it is different from word
  processing programs, spreadsheets, and all the other software programs on your computer.
  The OS is the computer’s master control program. The OS provides you with the tools
  (commands) that enable you to interact with the PC. When you issue a command, the OS
  translates it into code the machine can use. The OS also ensures that the results of your
  actions are displayed on screen, printed, and so on.
  When you turn on a computer, the machine looks for an operating system to boot before it
  runs any other programs. After the OS starts up, it takes change until you shut down the
  computer. The operating system performs the following functions:
       Provides the instructions to display the on-screen elements with which you interact.
         Collectively, these elements are known as the user interface.
       Loads programs (such as word processing and spreadsheet programs) into the
         computer’s memory so that you can use them.
       Coordinates how programs work with the CPU,RAM, keyboard, mouse, printer,
         and other hardware as well as with other software.
       Manages the way information is stored on and retrieved from disks.
  Parts of the Interface
        Figure shows the Windows 98 interface with the Start menu open, a program
  running, and a dialog box open. These features are discussed in the following section.

      Icons
                                                                              Window
                                                                              Control Buttons




                                                                              Program running
                                                                              in Window



                                                                                Dialog Box
  Start Menu




                                                                                Desktop

                                               Task Bar


Start Button

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  PREPARED BY M. ASIF NAEEM LECTURER BUITMS
INTRODUCTION TO COMPUTER                                                     LECTURE 07



The Desktop
Software makers call the colored area you see on screen the desktop because they want you
to think of it just as the surface of a desk. The pictures, too, stand for things you might have
in your office in the case of Window, My Computer, a Recycle Bin, an Inbox, and a
Briefcase These pictures are called icons, a word that means image. In this context, an icon
is an image that represents an object.
Icons
         Icons represent the parts of the computer you work with printers, fonts, document
files, folders (a way to organize files into logical groups), disk drives, programs, and so on.
Software designers try to make the icons look like what they represent, so it is easy to
identify the icon you need.
The Taskbar and the Start Button
Whenever you start a program in Windows 98/95, a button for it appears on the taskbar an
area at the bottom of the screen whose purpose is to display the buttons for the programs
you are running. When you have multiple programs running, you can shift from one to the
other by clicking a program’s button on the taskbar. The program in the foreground with
the highlighted button in the taskbar is called the active program.
Programs Running in Windows
       After you double-click a program icon to load a program into memory, when the
program appears, it may take up the whole screen or it may appear in a rectangular frame
on the screen, known as a window. By manipulating these windows on the desktop, you
can see multiple programs that have been loaded into memory at the same time.
Window Control Buttons
  In the top-right corner of a window in Windows 95/98 are three buttons for
manipulating the windows.
   You click the single line the Minimize button to reduce the program to a button
     on the taskbar.
   You click the picture of a box the Maximize button to restore the window to its
     previous size.
   You click the   the Close button – to close the window altogether.

Menus
       Although you initiate many tasks by clicking icons and buttons, you can also start
tasks by choosing commands from lists called menus. You have already seen the Start
menu, which appears when you click the Start button in Windows 95/98. The more
standard type of menu, however, appears at the top of many windows (in all the popular
GUL operating systems) in a horizontal list of menus called the menu bar. When you click
an item in the menu bar, a menu “drops down” and display a list of commands (for this
reason, these menus are sometimes called pull-down menus or drop-down menus).
Dialog Boxes
Dialog boxes are special-purpose windows that appear when you need to tell a program
(or the operating system) what to do next. For example, if you choose find and then choose
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PREPARED BY M. ASIF NAEEM LECTURER BUITMS
INTRODUCTION TO COMPUTER                                                    LECTURE 07

Files or Folders from the Windows Start menu, a dialog box appears, asking you to
describe the file or folder you want to find. A dialog box is called that because it conducts a
“dialog” with you as it seeks the information it needs to perform a task.
The Command-Line Interface
        The graphical user interface has become the standard because the Macintosh and
Windows operating systems use it. However, for more than a decade, computer operating
systems used command-line interfaces, which are environments that use type-written
commands rather than graphical objects to execute tasks and process data.
During the 1980s, the most popular of these were Microsoft’s MS-DOS and its near twin
PC-DOS from IBM. “DOS” is pronounced “doss” and stands for “Disk Operating System.”
Users interact with a command-line interface by typing strings of characters at a prompt
on screen. In DOS, the prompt usually includes the identification for the active disk drive
(a letter followed by a colon), a backslash (\), and a greater-than symbol, as in C:>.




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PREPARED BY M. ASIF NAEEM LECTURER BUITMS
INTRODUCTION TO COMPUTER                                                  LECTURE 07


RUNNING PROGRAMS
        Just as the operating system can provide a consistent interface for running programs
on the computer, it is also the interface between those programs and other computer
resources (such as computer memory, a printer, or another program such as a spreadsheet
application).
For example, when you want your word processing program to retrieve a file. You use the
Open dialog box to list the files in the folder that you specify.
Some other services that an operating system provides to programs, in addition to listing
files, are:
     Saving the contents of files to a disk for permanent storage
     Reading the contents of a file from disk into memory
     Sending a document to the printer and activating the printer
     Providing resources that let you copy or move data from one document to another,
        or from one program to another
     Allocating RAM among various programs that you may have open
     Recognizing keystrokes or mouse clicks and displaying characters or graphics on the
        screen

Sharing Information
       As soon as you begin using a word processing program or almost any other type of
application you discover the need to move chunks of data from one place in a document
to another. For example, you might look at a letter and realize that it would make more
sense if the second paragraph were moved to page 2. One of the beauties of using a
computer is that this type of editing is not only possible but simple.
Most operating systems, including Windows 95/98, Windows NT, and the Macintosh OS,
accomplish this feat with an operating system feature known as the Clipboard. The
Clipboard is a temporary storage space for data that is being copied or moved. For
example, to move a paragraph in a word-processed document, you perform. Often, instead
of using the Cut command, which removes data and places it on the Clipboard you may
want to use Copy, which makes a copy of the data and s6tores it on the Clipboard but does
not remove the original. In either case, you use the Paste command to copy the contents of
the Clipboard back into your document.
Note: The Clipboard stores only one set of data at a time, although the set of data can be
almost any size or length. The contents of the Clipboard are cleared each time you select a
new set of data and choose either the Cut or Copy commands again. This fact has two
important consequences:
    1. You must be careful not to erase valuable data that has been placed in the Clipboard
       or you will lose it.
    2. You can paste data from the Clipboard as many times as you like (until you choose
       Cut or copy again)
The versatility of the Clipboard has been further extended with a feature known in
Windows as OLE, which stands for Object Linking and Embedding. A simple cut and paste

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PREPARED BY M. ASIF NAEEM LECTURER BUITMS
INTRODUCTION TO COMPUTER                                                    LECTURE 07

between applications results in object embedding. The data, which is known as an object in
programming that was applied to it in the original application.

Multitasking
       Multitasking means much more than the capability to load multiple programs into
memory (although even that was difficult for earlier operating systems). Multitasking
mean being able to perform two or more procedures such as printing a multiage document,
sending e-mail over the Internet, and typing a letter all simultaneously.
Software engineers use two methods to develop multitasking operating systems. The first
requires cooperation between the operating system and application programs. Programs
that are currently running will periodically check the operating system to see whether any
other programs need the CPU. If any do, the running program will relinquish control of the
CPU to the next program. This method is called cooperative multitasking and is used by
the Macintosh and Windows 3.x operating systems to allow such activities as printing
while the user continues to type or use the mouse to input more data.
The second method is called preemptive multitasking. With this method, the operating
system maintains a list of programs that are running and assigns a priority to each program
in the list. The operating system can intervene and modify a program’s priority status,
rearranging the priority list. With preemptive multitasking, the operating system can
preempt the program that is running and reassign the time to a higher-priority task at any
time. Preemptive multitasking thereby has the advantage of being able to carry out higher
priority programs faster than lower-priority programs. Windows 95/98, Windows NT,
OS/2 and UNIX employ preemptive multitasking.

MANAGING FILES
       The files that the operating system works with may be programs or data files. Most
programs you purchase come with numerous files----some may even include hundreds.
When you use the programs, you often create your own data files, such as word processing
documents, and store them on a disk under names that you assign to them. A large hard
disk often holds thousands of program and data files. It is the responsibility of the
operating system to keep track of all these files so that it can copy any one of them into
RAM at a moment’s notice.
To accomplish this feat, the operating system maintains a list of the contents of a disk on
the disk itself. As you may recall, there is an area called the File Allocation Table, or FAT,
that the operating system creates when you format a disk. The operating system updates
the information in the FAT any time a file is created, moved, renamed, or deleted.




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PREPARED BY M. ASIF NAEEM LECTURER BUITMS
     INTRODUCTION TO COMPUTER                                                                LECTURE 07



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     MANAGING HRDWARE
            When programs run, they need to use the computer’s memory, monitor, disk drives,
     and other devices, such as a printer, modem, or CD-ROM drive. The operating system is
     the intermediary between programs and hardware. In a computer network, the operating
     system also mediates between your computer and other devices on the network.
     Processing Interrupts
            The operating system responds to requests to use memory and other devices, keeps
     track of which programs have access to which devices, and coordinates everything the
     hardware does so that various activities do not overlap and cause the computer to become
     confused and stop working. The operating system uses interrupt requests (IRQs) to help
     the CPU coordinate processes. For example, if you tell the operating system list the files in
     a folder, if sends an interrupt request to the computer’s CPU.




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     PREPARED BY M. ASIF NAEEM LECTURER BUITMS
INTRODUCTION TO COMPUTER                                                            LECTURE 07




       1 When you click on a
       folder,      the     OS
       interprets the action as
       a command to list the
       files in files in that                                                  7 The contents of the
       folder.                                                                 highlighted folder are now
                                                                               shown on the right side of the
                                                                               screen.




                                               4 The OS tells the
                                               CPU to go to the
                                               disk drive and
                                               retrieve the names
                                               of the files in the
                                               folder.
           2 The OS sends an
           interrupt request to                                              6 The OS intercepts the list
           the CPU.                                                          of file names returning from
                                                                             the disk drive and displays it
                                                                             on the screen.




                                                 5 The CPU retrieves the
           3   When possible, the CPU            names of the files in the
           pauses any other processing           folder.
           and checks with the OS to see
           what new processing job is
           being requested.




Drivers
        In addition to using interrupts, the operating system often provides complete
programs for working with special devices, such as printers. These programs are called
drivers because they allow the operating system and other programs to activate and use---
that is, “drive”---the hardware device. In the days when DOS reigned, drivers had to be
installed separately for each program used. With modem operating systems such as
Windows 95/98, Windows NT, and the Macintosh OS, drivers are an integral part of the
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PREPARED BY M. ASIF NAEEM LECTURER BUITMS
INTRODUCTION TO COMPUTER                                                LECTURE 07

operating system. This means that most of the software you buy will work with your
printer, monitor, and other equipment without requiring any special installation. For
example, many modems use the same unified driver in Windows 95\98. All that is
different is the setup information the operating system uses to configure the modem to
accommodate specific capabilities of each modem.
Networking
        On a network, usually each person has a separate PC with its own operating system.
The network server also has its own operating system, which manages the flow of data on
the file server and around the network. The leading network operating system for PCs
today is a system dedicated just to networking----Novell Intranet Ware. However,
Windows NT seems to be rapidly overtaking Intranet Ware (and its earlier versions, called
NetWare) as the predominant network-operating environment. As operating systems
continue to advance and evolve, networking will become an integral part of all operating
systems.




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PREPARED BY M. ASIF NAEEM LECTURER BUITMS

								
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