Chapter No 10
System Software and
software designed to operate and control
the computer hardware and to provide a
platform for running application software.
The programs that are part of the system
software include assemblers, compilers, file
An operating system is a program designed to run other programs
on a computer.
A computer’s operating system is its most important program.
It is considered the backbone of a computer, managing both
software and hardware resources.
Operating systems are responsible for everything from the control
and allocation of memory to recognizing input from external
devices and transmitting output to computer displays.
They also manage files on computer hard drives and control
peripherals, like printers and scanners.
Operating System Functions
Many different operating systems exist, designed
for all types of computers.
Regardless of the size of the computer, however,
most operating systems provide similar functions.
The operating system handles many of these
functions automatically, without requiring any
instructions from a user.
Some functions of operating systems are
discussed as under:
Operating System Functions
Starting and Shutting Down a Computer
The process of starting or restarting a computer is called booting.
Turning on a computer is called cold boot.
Warm boot is the process of using the operating system to restart a
Each time you boot a computer, the kernel and frequently
used operating system instructions are loaded, or copied,
from storage into the computer’s memory (RAM).
The kernel is the core of an operating system that manages
memory and devices, maintains the computer’s clock, starts
programs, and assigns the computer’s resources, such as
devices, programs, data, and information.
Operating System Functions
The steps in the following paragraphs explain what occurs during a
cold boot on a personal computer using the Windows operating
Step 1: When you turn on the computer, the power supply sends an
electrical signal to the components in the system unit.
Step 2: The charge of electricity causes the processor chip to reset itself
and find the ROM chip(s) that contains the BIOS. The BIOS, which stands
for basic input/output system, is firmware that contains the computer’s
Step 3: The BIOS executes a series of tests to make sure the computer
hardware is connected properly and operating correctly. The tests,
collectively called the power-on self test (POST ), check the various system
components including the buses, system clock, adapter cards, RAM chips,
mouse, keyboard, and drives. As the POST executes, LEDs (tiny lights)
flicker on devices such as the disk drives and keyboard.
Beeps also may sound, and messages may appear on the screen.
Operating System Functions
Step 4: The POST results are compared with data in a
CMOS chip. CMOS is a technology that uses battery
power to retain information when the computer is off.
semiconductor chip stores configuration information
about the computer, such as the amount of memory;
type of disk drives, keyboard, and monitor; the current
date and time; and other startup information. It also
detects any new devices connected to the computer. If
any problems are identified, the computer may beep,
display error messages, or cease operating —
depending on the severity of the problem.
Operating System Functions
Step 5: If the POST completes successfully,
the BIOS searches for specific operating
system files called system files. The BIOS
may look first to see if a USB flash drive
plugged in a USB port or a disc in an optical
disc drive contains the system files, or it may
look directly on drive C (the designation
usually given to the first hard disk) for the
Components of Computer
Step 6: Once located, the system files load into memory
(RAM) from storage (usually the hard disk) and execute.
Next, the kernel of the operating system loads into
memory. Then, the operating system in memory takes
control of the computer.
Step 7: The operating system loads system configuration
information. In the latest Windows versions, the registry
consists of several files that contain the system
A boot drive is the drive from which your personal
computer boots (starts). In most cases, drive C (the hard disk) is the
boot drive. Sometimes a hard disk becomes damaged and the
computer cannot boot from the hard disk, or you may want to
preview an operating system without installing it. In these cases,
you can boot from a special disk, called a boot disk or a recovery
disk, that contains a few system files that will start the computer.
Providing a User Interface
You interact with software through its user interface. That is, a user
interface controls how you enter data and instructions and how
information is displayed on the screen. Two types of user interfaces
are graphical and command-line. Operating systems often use a
combination of these interfaces to define how a user interacts with a
Graphical User Interface Most users
today work with a graphical user interface.
With a graphical user interface (GUI), you
interact with menus and visual images such as
buttons and other graphical objects to issue
commands. Many current GUI operating
systems incorporate features similar to those
of a Web browser, such as links and
navigation buttons (i.e., Back button and
To configure devices, manage system resources, and
troubleshoot network connections, network administrators
and other advanced users work with a command-line
interface. In a command-line interface, a user types
commands or presses special keys on the keyboard (such as
function keys or key combinations) to enter data and
instructions (Figure 8-5).
Some people consider command-line interfaces difficult to
use because they require exact spelling, grammar, and
punctuation. Command-line interfaces, however, give a user
more control to manage detailed settings. When working
with a command-line interface, the set of commands entered
into the computer is called the command language.
Some operating systems support a single user and only one running
program at a time.
Others support thousands of users running multiple programs.
A single user/single tasking operating system allows only one user
to run one program at a time.
Early systems were single user/single tasking. Smart phones and other
mobile devices, however, often use a single user/single tasking operating
A single user/multitasking operating system allows a single user to work
on two or more programs that reside in memory at the same time.
When a computer is running multiple programs concurrently, one program
is in the foreground and the others are in the background.
The one in the foreground is the active program, that is, the one you
currently are using. The other programs running but not in use are in the
The purpose of memory management is to optimize the
use of random access memory (RAM).
The operating system allocates, or assigns, data and
instructions to an area of memory while they are being
Then, it carefully monitors the contents of memory.
Finally, the operating system releases these items from
being monitored in memory when the processor no longer
If you have multiple programs running simultaneously, it
is possible to run out of RAM, the operating system may
have to use virtual memory to solve the problem.
With virtual memory, the operating system allocates a portion of a
storage medium, usually the hard disk, to function as additional
As you interact with a program, part of it may be in physical RAM,
while the rest of the program is on the hard disk as virtual memory.
Because virtual memory is slower than RAM, users may notice the
computer slowing down while it uses virtual memory.
The area of the hard disk used for virtual memory is called a swap
file because it swaps (exchanges) data, information, and instructions
between memory and storage. A page is the amount of data and
program instructions that can swap at a given time.
The technique of swapping items between memory and storage,
called paging, is a time-consuming process for the computer.
The operating system determines the order in which tasks are
processed. A task, is an operation the processor manages.
Tasks include receiving data from an input device, processing
instructions, sending information to an output device, and
transferring items from storage to memory and from memory
A multiuser operating system does not always process tasks on
a first-come, first-served basis.
Sometimes, one user may have a higher priority than other
users. In this case, the operating system adjusts the schedule of
Sometimes, a device already may be busy processing one task
when it receives a second task.
This occurs because the processor operates at a much faster
rate of speed than peripheral devices.
A driver, short for device driver, is a small program that
tells the operating system how to communicate with a
Each device on a computer, such as the mouse, keyboard,
monitor, printer, card reader/writer, and scanner, has its
own specialized set of commands and thus requires its
own specific driver. When you boot a computer, the
operating system loads each device’s driver. These devices
will not function without their correct drivers.
If you attach a new device to a computer, such as a printer
or scanner, its driver must be installed before you can use
Today, most devices and operating systems support
Plug and Play.
Plug and Play means the operating system
automatically configures new devices as you install
them. Specifically, it assists you in the device’s
installation by loading the necessary drivers
automatically and checking for conflicts with other
devices. With Plug and Play, a user plugs in a
device, turns on the computer, and then uses the
device without having to configure the system
manually. Devices that connect to a USB port on
the system unit typically are Plug and Play.
Operating systems typically contain a performance monitor. A
performance monitor is a program that assesses and reports
information about various computer resources and devices.
For example, users can monitor the processor, disks, network,
and memory usage.
The information in performance reports helps users and
administrators identify a problem with resources so that they
can try to resolve any problems. If a computer is running
extremely slow, for example, the performance monitor may
determine that the computer’s memory is being used to its
Thus, you might consider installing additional memory in the
Operating systems often provide users with
the capability of managing files, searching for
files, viewing images, securing a computer
from unauthorized access, uninstalling
programs, cleaning up disks, defragmenting
disks, diagnosing problems, backing up files
and disks, and setting up screen savers.
Updating Software Automatically
Many popular programs, including most operating
systems, include an automatic update feature
that automatically provides updates to the
program. With an operating system, these updates
can include fixes to program bugs, or errors,
enhancements to security, modifications to device
drivers, access to new or expanded components
such as desktop themes or games, and even
updates to application software on the computer
such as a Web browser.
Computer and network administrators typically
have an administrator account that enables them to
access all files and programs on the computer or
network, install programs, and specify settings that
affect all users on a computer or network.
Settings include creating user accounts and
establishing permissions. These permissions define
who can access certain resources and when they
can access those resources.
Controlling a Network
Some operating systems are designed to work with a server
on a network. A server operating system is an operating
system that organizes and coordinates how multiple users
access and share resources on a network.
Resources include hardware, software, data, and
information. For example, a server operating system
allows multiple users to share a printer, Internet access,
files, and programs.
Some operating systems have network features built into
them. In other cases, the server operating system is a set of
programs separate from the operating system on the client
computers that access the network.
Types of Operating Systems:
The three basic categories of operating systems that exist today
are stand-alone, server, and embedded.
stand-alone operating system is a complete operating
system that works on a desktop computer, notebook
computer, or mobile computing device. Some stand-alone
operating systems are called client operating systems because
they also work in conjunction with a server operating system.
Client operating systems can operate with or without a
network. Other stand-alone operating systems include
networking capabilities, allowing the home and small
business user to set up a small network.
Examples of currently used stand-alone operating systems
are Windows Vista, Mac OSX, UNIX, and Linux.
Server Operating Systems
A server operating system is an operating system that is
designed specifically to support a network.
A server operating system typically resides on a server. The
client computers on the network rely on the server(s) for
To meet the needs of all sizes of businesses, the
Windows Server 2008 family includes many editions, with the
more common listed below:
• Windows Server 2008 Standard for the typical small- to
medium-sized business network
• Windows Server 2008 Enterprise for medium to large-sized
businesses, including those with e-commerce operations
• Windows Server 2008 Datacenter for businesses with huge
volumes of transactions and large-scale databases.
Embedded Operating Systems
The operating system on mobile devices and
many consumer electronics, called an
embedded operating system, resides on a
Popular embedded operating systems today
include Windows Mobile, Palm OS, iPhone
OS, BlackBerry, embedded Linux, and
Application software is all the computer software
that causes a computer to perform useful tasks beyond the
running of the computer itself. Also known as software
application, application program or application.
The term is used to contrast such software with system
software, which manages and integrates a computer's
capabilities but does not directly perform tasks that
benefit the user. The system software serves the
application, which in turn serves the user.
In information technology, an application is a
computer program designed to help people
perform an activity. An application thus differs
from an operating system (which runs a computer),
a utility (which performs maintenance or generalpurpose chores), and a programming tools (with
which computer programs are created).
enterprise software, graphics software, media
players, and office suites. Many application
programs deal principally with documents.
Applications may be bundled with the computer
and its system software or published separately.
Application software classification
There are many types of application software:
An application suite consists of multiple applications bundled
together. They usually have related functions, features and user
interfaces, and may be able to interact with each other, e.g. open
each other's files. Business applications often come in suites, e.g.
Microsoft Office, and iWork, which bundle together a word
processor, a spreadsheet, etc.; but suites exist for other purposes, e.g.
graphics or music.
Enterprise software addresses the needs of an entire organization's
processes and data flow, across most all departments, often in a
large distributed environment. (Examples include financial systems,
customer relationship management (CRM) systems and supply
chain management software).
Enterprise infrastructure software provides common
capabilities needed to support enterprise software systems.
(Examples include databases, email servers, and systems for
managing networks and security.)
Information worker software lets users create and manage
information, often for individual projects within a department, in
contrast to enterprise management. Examples include time
analytical, and collaborative. Word processors, spreadsheets, email
and blog clients, personal information system, and individual media
editors may aid in multiple information worker tasks.
simulates physical or abstract systems
for either research, training or entertainment purposes.
Media development software
electronic media for others to consume, most often in a commercial
or educational setting. This includes graphic-art software, desktop
publishing software, multimedia development software, HTML
composition, and many others.
Product engineering software is
used in developing hardware and software
products. This includes computer-aided
design (CAD), computer-aided engineering
(CAE), computer language editing and
compiling tools, integrated development
environments, and application programmer