VIPS/BBA/COMPUTER FUNDAMENTALS/UNIT 3

OPERATING SYSTEM

An operating system (OS) is a collection of software that manages computer

hardware resources and provides common services for computer programs. The operating system
is a vital component of the system software in a computer system. Application programs require
an operating system to function.
An operating system is a program that acts as an interface between the user and the computer
hardware and controls the execution of all kinds of programs.

Following are some of important functions of an operating System.

 Memory Management
 Process Management
 Device Management
 File Management
 Security
 Command Interpretation

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Types of operating system

1) Serial Processing

The earliest computer system has no OS at all, and is characterized as serial processing
because users have to reserve time slots in advance and during the allotted period, they
occupy the computer exclusively. Thus the computer will be used in sequence by different
users.

These early systems presented 2 Major problems:

1) Users may finish their task earlier than you have expected and unfortunately the rest time
is simply wasted or they cannot finish in the allotted time and thus are forced to stop
which may cause inconvenience.
2) In such systems, Programs are presented by Cards. Programs are loaded into memory via
card reader. With no OS available users have to manually load the compiler program first
with the user program as input. If an error occurred the user has to repeat the whole
process from the beginning. Thus much time is wasted.

2) Simple Batch Systems

 In this type of system there is no direct interaction between the user and the computer.
 The user has to submit a job (written on card or tape) to a computer operator.
 Then the computer operator places a batch of several jobs on an input device.
 Jobs are batched together by type of languages and requirement.
 Then a special program the monitor, manages the execution of each program in the batch.
 The monitor is always in the main memory and available for execution.

Following are some disadvantages of this type of system:

1) Zero interaction between user and computer.

2) No mechanism to prioritize processes.

3) Multiprogrammed Operating system

Even with the automatic job processing by a monitor, the processor is still often idle. The
problem is actually what we have discussed before regarding programmed I/O.That is
program may have to wait for I/O operation finish and thus leads to the processor’s idling.
The solution is to run multiple programs concurrently during a certain period so that
whenever the current program has to wait for I/O devices, control may be transferred to
another program. If needed, a third program may be loaded or even more.

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This scheme is called multiprogramming. With multiprogramming, the utilization of

processor is greatly improved, but it has its own problems. To run multiple programs
concurrently, the memory should be organized properly so that each program has its own
space and does not invade others. At some moment there may be more than one program
ready to run. Thus some form of scheduling is needed to obtain better performance.

4) Distributed operating System

A distributed system is a collection of independent computers, interconnected via a network,

capable of collaborating on a task. Distributed systems use multiple independent computers
to serve multiple real time application and multiple users. Data processing jobs are
distributed among the computers accordingly to which one can perform each job most
efficiently.

The computers communicate with one another through various communication lines (such as
high-speed buses or telephone lines). These are referred as loosely coupled systems or
distributed systems.

The advantages of distributed systems are following.

 With resource sharing facility user at one site may be able to use the resources available
at another.
 Speedup the exchange of data with one another via electronic mail.
 If one site fails in a distributed system, the remaining sites can potentially continue
operating.
 Better service to the customers.
 Reduction of the load on the host computer.
 Reduction of delays in data processing.

Examples of distributed systems are telephone networks, cellular networks, ATM machines
etc.

5) Real Time operating System

Real time system is defined as a data processing system in which the time interval required to
process and respond to inputs is so small that it controls the environment. The time taken by
the system to respond to an input and display of required updated information is termed as
response time. So in this method response time is very less as compared to the online
processing.

Real-time systems are used when there are rigid time requirements on the operation of a
processor or the flow of data and real-time systems can be used as a control device in a

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dedicated application. Real-time operating system has well-defined, fixed time constraints
otherwise system will fail. For example scientific experiments, medical imaging systems,
industrial control systems, weapon systems, robots, and home-appliances controllers, Air
traffic control system etc.

There are two types of real-time operating systems.

Hard real-time systems

Hard real-time systems guarantee that critical tasks complete on time. In hard real-time
systems secondary storage is limited or missing with data stored in ROM. In these systems
virtual memory is almost never found.

Soft real-time systems

Soft real time systems are less restrictive. Critical real-time task gets priority over other tasks
and retains the priority until it completes. Soft real-time systems have limited utility than
hard real-time systems. For example, Multimedia, virtual reality, Advanced Scientific
Projects like undersea exploration and planetary rovers etc.

6) Multiprocessing Operating System

Generally a Computer has a Single Processor means the Computer have a just one CPU for
Processing the instructions. But if we are Running multiple jobs, then this will decrease the
Speed of processing. For Increasing the Speed of Processing we use the Multiprocessing
Operating System. In the Multi Processing there is two or More CPU in a Single Computer
System. If one CPU will fail, then other CPU is used for providing backup to the first CPU.
With the help of Multi-processing, we can Execute Many Jobs at a Time. In such a system
instructions from different and independent programs can be processed simultaneously by
different CPUs or the CPUs may simultaneously execute different instructions from the same
program. If first CPU Completed his Work before the Second CPU, then the Work of Second
CPU will be divided into the First and Second.
Multiprocessing systems are of two types- tightly coupled systems and loosely coupled
systems. In tightly coupled systems there is a single wide primary memory which is shared
by all the processors. On the other hand in loosely coupled systems the processors do not
share memory and each processor has its own local memory.

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7) Multitasking/Time Sharing

The ability to execute more than one task at the same time, a task being a program. The terms
multitasking and multiprocessing are often used interchangeably, although multiprocessing
implies that more than one CPU is involved.

In multitasking, only one CPU is involved, but it switches from one program to another so
quickly that it gives the appearance of executing all of the programs at the same time.

There are two basic types of multitasking: preemptive and cooperative. In preemptive
multitasking, the operating system parcels out CPU time slices to each program. In
cooperative multitasking, each program can control the CPU for as long as it needs it. If a
program is not using the CPU, however, it can allow another program to use it temporarily.
OS/2, Windows 95, Windows NT, the Amiga operating system and UNIX use preemptive
multitasking, whereas Microsoft Windows 3.x and the MultiFinder (for Macintosh
computers) use cooperative multitasking.

8) Embedded Operating System

It is an operating system for embedded computer systems. These operating systems are
designed to be compact, efficient and reliable forsaking many functions that non embedded
computer operating systems provide, and which may not be used by the specialized
applications they run. They are designed to operate on small machines like PDAs. They are
able to operate with a limited number of resources. They are very compact and extremely
efficient by design. They are frequently also referred to as real time operating systems
(RTOS). Windows CE and Minix 3 are some of the examples of embedded operating system.

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BOOTING

Boot
It is the process of starting or resetting a computer. When the computer is first turned on(cold boot) or
reset(warm boot),the computer executes the software that loads and starts the computer OS and prepares it
for use.

Boot Record
It refers to the section of disk that contains the operating system. Boot sector is the portion of the disk
reserved for self starting portion (Bootstrap loader) of an operating system.

Boot strap loader

It is a program that is automatically run when computer is switched on. It first performs few hardware
tests then passes control to operating system’s loader files to load the OS.

How does booting work? : Start-Up Sequence

Steps:
1. As soon as the computer is turned on, the internal power supply turns on and initialises.The basic
input-output system (BIOS) on system’s read only memory (ROM) chip is “woken-up” and takes charge.
BIOS is already loaded because it’s built-in to the ROM chip and unlike RAM, ROM contents don't get
erased when the computer is turned off.

2. The BIOS performs the Power-on self test (POST) to make sure all computers components are
operational. If there are any errors, the boot process stops.

3. The BIOS looks for video card. In particular it looks for video card’s built in BIOS program and runs
it.

4. The BIOS begins the search for a drive to boot from. Most modern BIOSes contain a setting that
controls if the system should try to boot from floppy disk (A:) or first try the Hard disk(C:). Some BIOSes
will even let user to boot from CD-ROM drive or other devices, depending on the boot sequence BIOS
setting. If no boot device at all can be found, the system will normally display an error message and then
freeze up the system.

5. Having identified its target boot drive, the BIOS looks for the boot information to start the operating
system boot process. If it is searching a hard disk, it looks for boot record or master boot record at
cylinder 0, head 0, and sector 1(the first sector on the disk)

6. It then loads the boot record into a specific place in RAM.

7. The BIOS displays its startup screen. The boot record contains a program that BIOS now branches to,
giving the boot record control of the computer.

8. The boot record loads the initial system file (for example, for DOS system,IO.SYS) into RAM from
the diskette or hard disk. Another special file that is loaded is the one that tells which specific applications
or commands the user wants to have included or performed as part of the boot process.

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9. One of the first operating system files that is loaded is a system configuration file (for DOS,its called
CONFIG.SYS). Information in the configuration file tells the loading program which specific operating
system files need to be loaded for specific device such as driver.

10. The BIOS performs a “system inventory “of sorts, doing more tests to determine what sort of
hardware is in the system.

11. If the BIOS support the Plug and Play standard, it will detect and configure Plug and Play devices at
this time and display a message on the screen for each one it finds.

12. The BIOS will display a summary screen about system’s configuration it flashes on the screen very
quickly before scrolling off the top.

System Configuration
System configuration is the process of setting up Hardware devices and assigning resources to them so
that they work together without problems. A properly-configured system allows user to avoid nasty
resource conflict problems, and makes it easier for the user to upgrade system with new equipment in the
future. An improperly configured system may lead to strange errors and problems, and makes upgrading
difficult.

Directory
A directory is an organizational unit, or container, used to organize folders and files into
a hierarchical structure. Directories contain bookkeeping information about files that are, figuratively
speaking, beneath them in the hierarchy. You can think of a directory as a file cabinet that contains
folders that contain files. Many graphical user interfaces use the term folder instead of directory.

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File

A collection of data or information that has a name, called the filename. Almost all information stored in
a computer must be in a file. There are many different types of files: data files, text files,
program files, directory files, and so on. Different types of files store different types of information. For
example, program files store programs, whereas text files store text.

Volume

Volume refers to a tape or disk that stores computer data. Sometimes large hard disks are divided into
several volumes (called partitions), each of which is treated as separate disk. In computers, a volume is an
identifiable unit of data storage that is sometimes physically removable from the computer or storage
system. Each volume has a system-unique name or number that allows it to be specified by a user.

Volume Label

Volume Label refers to the name for a disk or tape. For mass storage devices, a label is the name of a
storage volume. It is sometimes referred as to volume label. It is an area on tape or disk that is used to
identify the tape volume and its owner.

A volume label is basically the name we assign to the drive. Example: - C: Drive has a volume label
Cicero, D: drive has volume label Darwin, E: drive has volume label Emmanuelle and so on

Difference between CUI and GUI

TOPIC COMMAND LINE GUI

New users find it much more difficult to Although new users may have a
use the command line interface as difficult at time learning to use the
memorization of the commands needs to mouse to operate and use a GUI most
be done. Moreover, each and every part users pick up this interface much easier
Ease of the command needs to be typed by the when compared to a command line
user. interface.

Users using command line interface get Although GUI provides a lot of control
much more control over the operating over the file system and the operating
system and the file system. For example, system, even then the advanced users
a single line command may be used to need the command line at some point
Control copy a file from one location to the of time for advanced level tasks.
other.

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Although CUI provides multitasking to a The windowed architecture of GUI

Multitasking great extent, but there is no provision for provides for viewing more than one
viewing all those tasks on the same task on the screen at once hence the
terminal. efficiency of the user increases.

Because command line users only need A GUI may be easier to use because of
to use their keyboards to navigate a the mouse. However, using a mouse
command line interface and often only and keyboard to navigate and control
Speed need to execute a few lines to perform a your operating system for many
task an advanced command line interface things is going to be much slower than
user would be able to get something someone who is working in a
done faster then an advance GUI user. command line.

A lot less computer resources are needed A lot more system resources are
when the system is running only required in case of GUI because of
command line interface. each of the elements that need to be
Low resources loaded such as icons, fonts, etc. In
addition video drivers, mouse drivers,
and other drivers that need to be loaded
will also take additional resources.

A sequence of commands to perform a A GUI doesn’t even come closer to

Scripting task or execute a program may easily be what is provided by CUI for scripting.
scripted using a command line interface. But it does provide for links, shortcuts,
etc.

Often when accessing another computer Although remote graphical access is

or networking device over a network a becoming popular and is possible. Not
Remote access user will only be able to manipulate the all computers and especially not all
device or its files using a command line, network equipment will have this
CLI, or other text only manipulation. ability.

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