The document discusses operating systems and provides definitions and examples of different types of operating systems, including batch, time-sharing, distributed, network, and real-time operating systems. It also covers file systems, DOS commands, batch files, and the history of DOS. The key points covered include definitions of an operating system and its main functions, examples of popular operating systems like Linux and Windows, and characteristics of different types of operating systems.

1. Unit III
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2. Operating System : Definition
 An Operating System (OS) is an interface between a
computer user and computer hardware.
 An operating system is a software which performs all
the basic tasks like file management, memory
management, process management, handling input
and output , and controlling peripheral devices such as
disk drives and printers.
 Some popular Operating Systems include Linux
Operating System, Windows Operating System etc.
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3. Operating System:Diagram
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4. Some of important functions of an
operating System are:
 Memory Management
 Processor Management
 Device Management
 File Management
 Security
 Control over system performance
 Job accounting
 Error detecting aids
 Coordination between other software and users
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5. Few common services provided by
an operating system:
 Program execution
 I/O operations
 File System manipulation
 Communication
 Error Detection
 Resource Allocation
 Protection
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6. Operating System ─ Types
1.Batch Operating System
 The users of a batch operating system do not interact
with the computer directly.
 Each user prepares his job on an off-line device like
punch cards and submits it to the computer operator.
 To speed up processing, jobs with similar needs are
batched together and run as a group.
 The programmers leave their programs with the
operator and the operator then sorts the programs
with similar requirements into batches.
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7. Cont…
 The problems with Batch Systems are as follows:
i )Lack of interaction between the user and the job.
ii) CPU is often idle, because the speed of the
mechanical I/O devices is slower than the CPU.
iii)Difficult to provide the desired priority.
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8. Cont…
2.Time-sharing Operating Systems
 Time-sharing is a technique which enables many people,
located at various terminals, to use a particular computer
system at the same time.
 Time-sharing or multitasking is a logical extension of
multiprogramming.
 Processor's time which is shared among multiple users
simultaneously is termed as time-sharing.
 The operating system uses CPU scheduling and
multiprogramming to provide each user with a small
portion of a time.
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9. Advantages of Timesharing are:
 Provides the advantage of quick response
 Avoids duplication of software
 Reduces CPU idle time
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10. Disadvantages of Time-sharing are:
 Problem of reliability
 Question of security and integrity of user programs
and data
 Problem of data communication
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11. Cont…
 3. Distributed Operating System
 Distributed systems use multiple central processors to
serve multiple real-time applications and multiple users.
 The processors 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.
 Processors in a distributed system may vary in size and
function.
 These processors are referred as sites, nodes, computers,
and so on.
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12. The advantages of distributed
systems are :
 With resource sharing facility, a 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.
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13. Cont…
4.Network Operating System
 A Network Operating System runs on a server and
provides the server the capability to manage data,
users, groups, security, applications, and other
networking functions.
 The primary purpose of the network operating system
is to allow shared file and printer access among
multiple computers in a network, typically a local area
network (LAN), a private network or to other
networks.
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14. Cont…
 Examples of network operating systems include
Microsoft Windows Server 2003, Microsoft Windows
Server 2008, UNIX, Linux, Mac OS X, Novell NetWare,
etc.
 The advantages of network operating systems are
as follows:
 Centralized servers are highly stable.
 Security is server managed.
 Upgrades to new technologies and hardware can be
easily integrated into the system.
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15. Cont...
 The disadvantages of network operating systems
are as follows:
 High cost of buying and running a server.
 Dependency on a central location for most operations.
 Regular maintenance and updates are required.
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16. Cont…
 5. Real-Time Operating System
 A 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 the response time.
 So in this method, the response time is very less
as compared to online processing.
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17. Cont….
 Real-time operating system must have well-defined, fixed
time constraints, otherwise the system will fail. For
example, Scientific experiments, medical imaging systems,
industrial control systems, weapon systems, robots, air
traffic control systems, etc.
 There are two types of real-time operating systems.
1. 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 and the data is stored in ROM.
In these systems, virtual memory is almost never found.
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18. Cont…
2. Soft real-time systems
Soft real-time systems are less restrictive. A 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.
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19. Operating System ─ File System
 A file is a named collection of related information that
is recorded on secondary storage such as magnetic
disks, magnetic tapes and optical disks.
 In general, a file is a sequence of bits, bytes, lines or
records whose meaning is defined by the files creator
and user.
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20. File Type
 File type refers to the ability of the operating system to
distinguish different types of file such as text files source
files and binary files etc.
 Operating system like MS-DOS and UNIX have the
following types of files:
1. Ordinary files
 These are the files that contain user information.
 These may have text, databases or executable program.
 The user can apply various operations on such files like
add, modify, delete or even remove the entire file.
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21. Cont…
2. Directory files
 These files contain list of file names and other
information related to these files.
3. Special files
 These files are also known as device files. These files
represent physical device like disks, terminals,
printers, networks, tape drive etc.
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22. DOS-History
 DOS is a family of disk operating systems primarily
consisting of MS-DOS and a rebranded version under
the name IBM PC DOS which were introduced in 1981.
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23. DOS commands
 ATTRIB
Change file attributes. + adds an attribute, - removes
it. Attributes are: A=archive; R=read only; S=system;
H=hidden.
 C:
Go to the C: drive. Similarly A: and D: etc.
 CD
Change directory. When you change directory, the
prompt changes, showing the path of the directory you
are currently in.
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24. Cont….
 CLS
Clear the screen.
 DEL
Delete one or more files in the current directory. Can
be used with the * and the ? wildcards.
 DIR
Displays the contents of a directory (folder).
 EDIT
Runs DOS EDIT (a simple text editor). Useful for
editing batch files and viewing logs. This command
requires QBASIC.EXE to be present.
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25. Cont….
 MD
Make Directory creates a new directory below the
current one. (The command can also be written
asMKDIR.)
 HELP
Displays DOS Help. For help on an individual
command, type HELP then the command for which
you want more information.
 PRINT
Prints the specified file (if the printer is supported in
DOS - many are not).
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26. Cont…
 RD
Remove directory. Removes a sub-directory of the
current directory. The directory you want to remove
must be empty of all files. (The command can also be
written as RMDIR)
 RENAME
Rename a file. You must use the full file name
including the suffix.
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27. Batch Files
A batch file is a kind of script
file in DOS, OS/2 and Microsoft Windows. It consists
of a series of commands to be executed by
the command-line interpreter, stored in a plain
text file.
The filename extension .bat is
used in DOS and Windows. A batch file is a
text file that contains a sequence of commands for a
computer operating system.
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28. Cont…
 It's called a batch file because it batches (bundles or
packages) into a single file a set of commands that
would otherwise have to be presented to the system
interactively from a keyboard one at a time.
 A batch file is usually created for command sequences
for which a user has a repeated need. Commonly
needed batch files are often delivered as part of an
operating system.
 You initiate the sequence of commands in the batch
file by simply entering the name of the batch file on a
command line.
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29. Thank you
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