Lecture 11

INTRODUCTION TO COMPUTER LECTURE 11

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

1

INTRODUCTION TO COMPUTER LECTURE 11

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 2

INTRODUCTION TO COMPUTER LECTURE 11 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:>.

3

INTRODUCTION TO COMPUTER LECTURE 11

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

4

INTRODUCTION TO COMPUTER LECTURE 11 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.

5

INTRODUCTION TO COMPUTER LECTURE 11

C:

Applic -

Budge t-s

ation

1997

1998

HQ Project

Correspondenc e

Busin -ess

Private

In Box

Config

Word Proccesing

Sprea d-

Prese n-

Grap h-ics

Internet

E-mail

Web

Out Box

Trash

Windows

FTP

Fonts

Help

MS Apps

Start Menu

System

MS Draw

Text Conv

W ord

Color

Losu b-sys

VM M32

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.

6

INTRODUCTION TO COMPUTER LECTURE 11

1 When you click on a folder, the OS interprets the action as a command to list the files in files in that folder.

7 The contents of the 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

6 The OS intercepts the list of

interrupt request to the CPU.

3

When possible, the CPU pauses any other processing and checks with the OS to see what new processing job is being requested.

file names returning from the disk drive and displays it on the screen.

5 The CPU retrieves the names of the files in the folder.

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 7

INTRODUCTION TO COMPUTER LECTURE 11 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.

8