Operating System


4.2   Operating System

The operating system is the core software component of the computer. It performs many functions and is, in very basic terms, an interface between computer and the outside world. In the section about hardware, a computer is described as consisting of several component parts including your monitor, keyboard, mouse, and other parts. The operating system provides an interface to these parts using what is referred to as "drivers". This is why sometimes when you install a new printer or other piece of hardware, your system will ask you to install more software called a driver.

All computers need some sort of Operating System (OS). The majority of modern home computers use some form of Microsoft's operating systems. The original Microsoft operating system was called DOS (Disk Operating System) though most computers use Windows. Windows comes in various versions beginning with version 3.x then 95, 98, ME and currently XP. Some computer professionals, Internet Service Providers (ISP) and mainframe computer users use an operating system such as UNIX (or a variant such as Linux), Windows NT or 2000 (Win2k) or one of the other network or server based operating systems.

Device Driver

A driver is a specially written program which understands the operation of the device it interfaces to, such as a printer, video card, sound card or CD ROM drive. Typically this constitutes an interface for communicating with the device, through the specific computer bus or communications subsystem that the hardware is connected to, providing commands to and/or receiving data from the device, and on the other end, the requisite interfaces to the operating system and software applications.

Functions of Operating Systems

a. Process Management

This module Takes care of creation and deletion of processes, scheduling of system resources to different processes requesting them and providing synchronization and communication among processes. In a desktop environment, batch files can be written to perform a sequence of operations that can be scheduled to start at a given time.

b. Memory Management

It takes care of allocation and de-allocation of memory space to programs in need of this resource. Since the early days of computing, there has been a need for more memory than exists physically in a system. Virtual memory is used to overcome this limitation. Virtual memory makes the system appear to have more memory than it actually has by sharing it between competing processes as they need it.

The memory management subsystem provides:

Large Address Spaces

The operating system makes the system appear as if it has a larger amount of memory than it actually has. The virtual memory can be many times larger than the physical memory in the system.


Each process in the system has its own virtual address space. These virtual address spaces are completely separate from each other and so a process running one application cannot affect another. Also, the hardware virtual memory mechanisms allow areas of memory to be protected against writing. This protects code and data from being overwritten by rogue applications.

Memory Mapping

Memory mapping is used to map image and data files into a processes address space. In memory mapping, the contents of a file are linked directly into the virtual address space of a process.

Fair Physical Memory Allocation

The memory management subsystem allows each running process in the system a fair share of the physical memory of the system.

Shared Virtual Memory

Although virtual memory allows processes to have separate (virtual) address spaces, there are times when you need processes to share memory. For example there could be several processes in the system running the bash command shell. Rather than have several copies of bash, one in each processes virtual address space, it is better to have only one copy in physical memory and all of the processes running bash share it. Dynamic libraries are another common example of executing code shared between several processes.

c. File Management

File management module takes care of file related activities such as organization, storage, retrieval, naming, sharing and protection of files. The application program deals with data by file name and a particular location within the file. The operating system's file system knows where that data are physically stored (which sectors on disk) and interaction between the application and operating system is through the programming interface. Whenever an application needs to read or write data, it makes a call to the operating system.

d. Task Management

Multitasking, which is the ability to simultaneously execute multiple programs, is available in all operating systems today. Critical in the mainframe and server environment, applications can be prioritized to run faster or slower depending on their purpose. In the desktop world, multitasking is necessary for keeping several applications open at the same time so you can bounce back and forth among them.

e. Device Management

Device management controls peripheral devices by sending those commands in their own proprietary language. The software routine that knows how to deal with each device is called a "driver," and the OS requires drivers for the peripherals attached to the computer. When a new peripheral is added, that device's driver is installed into the operating system.

f. Security

Operating systems provide password protection to keep unauthorized users out of the system. Some operating systems also maintain activity logs and accounting of the user's time for billing purposes. They also provide backup and recovery routines for starting over in the event of a system failure.

One of the operating system is explained below is the most commonly used in modern computers today.

4.2.1 Windows



The desktop is the main screen area that one sees after he turn on a computer and log on to Windows. Like the top of an actual desk, it serves as a surface for a work. When one open Programs or folders then they appear on the desktop. One can also put things on the desktop, such as files and folders, and arrange them however, he wants. The desktop is sometimes defined more broadly to include the taskbar and Windows Sidebar.


Icons are small pictures that represent files, folders, programs, and other items. On the desk top from the upper left to the lower left side of the screen, there are small pictures or images called icons. Each one is used to make the computer do something.


The taskbar is the long horizontal bar at the bottom of a screen. Unlike the desktop, which can get obscured by the windows on top of it, the taskbar is visible almost all the time. It has four main sections:

  • The Start button, which opens the Start menu
  • The Quick Launch toolbar, which lets one start programs with one click.
  • The middle section, which shows programs and documents opened and allows to quick switching between them.
  • The notification area, which includes a clock and icons (small pictures) that communicate the status of certain programs and computer settings.

Start button

The start button is a very important and the most used part of Windows, clicking on the start button opens up the start menu; the start menu gives the major computer headings. These headings provide access to the major programs on computer such as access to program, settings, printers and many more.


Of the various assignments, one can perform on the computer desktop; it also provides many categories of objects. These objects allow one to perform available actions. The actions we can perform on the computer may depend on the object on which the action is performed and various other options. One of the objects the computer provides is called a menu. Moving the mouse over the items in the menu causes them to highlight.  Clicking on a highlighted item will open that program.

The Window Frame

Whenever user opens a program, file, or folder, it appears on the screen in a box of frame called a window (that’s where the Windows operating system gets its name). Each one of the most of the objects used when interacting with the computer is called a window. As a visible object a window is defined by its location on the screen and its dimensions with regards to the monitor screen as a whole.

Parts of a window frame:

  • Title bar:  Displays the name of the document and program (or the folder name if you’re working in a folder).
  • Minimize, Maximize, and Close buttons.  These buttons hide the window, enlarge it to fill the whole screen, and close it, respectively.
  • Menu bar: Contains items that you can click to make choices in a program.
  • Scroll bar: Lets you scroll the content of the window to see information that is currently out of view.
  • Borders and corners: One can drag these with mouse pointer to change the size of the   window.

Windows Control

Dialog Boxes

A Dialog Box is a square or rectangular window whose main role is to carry, hold, or host, other windows. By itself, a dialog box means nothing

Command Buttons

A command button, commonly called a button, is a rectangular object that displays a word or a group of words, expecting to make a decision. User makes decision by clicking the button. The button is usually placed on a dialog box but it can also be placed on another type of container.

Text Boxes

A text box is a window that is used to display text or to receive text from you. The type of text it displays or the type of the text you are asked to provide depends on the application or the situation.

The Scroll Bars

A scroll bar is an object that is used to navigate from one end of window content to another. There are two types of scroll bar: vertical and horizontal.

  • A vertical scroll bar allows navigating up and down to display a hidden section of a document.
  • A horizontal scroll bar allows navigating left and right on the document.

List Boxes

A list box is a rectangular control that displays a list of items. If you see that item that is convenient to the issue at hand, then you can click it. Once an item is clicked, it becomes highlighted, indicating that the item has been selected.

Combo Boxes

A combo box is a combination of a text box and a list box but is made of three sections. Based in its variations, there are three types of combo boxes:

The Drop down Combo Box:  One of the types of combo boxes is referred to a Drop Down. This control is made of a text box on the left side and a down-pointing arrowed button on the right side. Depending on how the control was created, when it comes up, it may not display anything.

The Drop down List Combo Box: Another type of combo box is referred to as Drop down List. This type also is made of a text box on the left and a down-pointing arrowed button on the right side. It also may appear empty when it comes up, depending on how it was created. The biggest difference between a drop down combo box and a drop down list combo box is that, with the drop down list, you can only select from the list: you cannot type anything in the text box part of the control.

The Simple Combo Box: The last type of combo box is called a simple combo box. This type of combo box is also made of two parts but they are distinct. The top section of the combo box displays a text box, immediately under the text box, there is a list box.


A toolbar provides a quick access to the most frequently used actions performed using the menu. A toolbar offers these items as buttons.

Status Bar

The Status Bar helps as a guide to the users of an application. In a typical application, it displays small sentences that further explain the role of a particular button or an action that are about to be perform. The messages that appear on the Status Bar vary from one application to another and depend on the position of the mouse on an application.


  • Both Windows and Mac have a number of tools built in to assist in solving computer problems.
  • Choosing Help allow Window users to access Troubleshooting Wizards that provide step-by-step suggestions.
  • System Information under System Tools provides valuable information and access to other system tools in Window.
  • System Profiler under Application, Utilities provide information about the Mac.
  • Running a Disk Scan occasionally or on a schedule can solve many simple errors.