OS AND THE SERVICES

1. OPERATING SYSTEM &
SERVICES IN OPERATING SYSTEM

2. SUB TOPICS:
• Definition of operating system
• Services provided by operating system.
• Types of O.S
• Features of Windows and Linux
• Files and Directories
• Internal and External Commands of DOS
• Batch Files

3. DEFINITION(SUB COMPONENTS):
Objectives Characteristics Features

4. DEFINITION:
• A operating system is a program that acts as an
interface between the software and the computer
hardware.
• A operating system is a computer program that
manages the resources of a computer.
• An operating system is a software that communicates
with the hardware and allows other programs to run.

5. OBJECTIVES:
• To provide users a convenient interface to use the computer
system.
• Manage the resources of a computer system.
• Making a computer system convenient to use in an efficient
manner.
• The efficient and fair sharing of resources among users and
programs.
• To hide the details of the hardware resources from the users.
• To acts as an intermediary between the hardware and its users
and making it easier for the users to access and use other

6. CHARACTERISTICS:
• Operating system is a collection of programs those are
responsible for the execution of other programs.
• It is responsible for controlling all the input and output devices
those are connected to the system.
• It is responsible for running all the application software’s.
• Provides scheduling to various processors means allocates the
memory to various process those who want to execute.
• Provides the communication between the user and the system.

7. FEATURES:
1. Software and Hardware management
2. Constant API( Application Program Interface)
3. Execution of Programs
4. Interruptions
5. Managing Memory
6. Networking
7. Security

8. NEED:
Users
Application
program
System
program
Operatin
g system
Computer
hardware

9. SOME OF THE IMPORTANT REASONS WHY DO WE
NEED AN OPERATING SYSTEM ARE AS FOLLOWS:
• Operating System provides an environment for running user
programs.
• It provides an interface to the user to communicate with the
system.
• User interacts with the computer through operating system in
order to accomplish his/her task since it is his primary
interface with a computer.
• It helps the user to understand the inner functions of a
computer very closely.

11. COMPONENTS OF OPERATING SYSTEM:
1. The hardware: CPU, Memory and Input/output devices.
2. The application programs: Word processors,
Spreadsheets,Compilers,Web Browsers Etc. are the examples
of application programs
3. Operational Users: Operational Users are the users
responsible for installation of the software (maintenance &
making available to the user).
4. End user: End Users are the actual users of the applications.

12. OPERATING SYSTEM SERVICES:
• · Program execution
• · I/O operations
• · File System manipulation
• · Communication
• · Error Detection
• · Resource Allocation
• · Protection

13. • Program Execution :
Operating systems handle many kinds of activities from user
programs to system programs like printer spooler, name servers,
file server, etc. Each of these activities is encapsulated as a
process.
• Loads a program into memory
• Executes the program
• Handles program's execution
• Provides a mechanism for process synchronization
• Provides a mechanism for process communication
• Provides a mechanism for deadlock handling

14. I/O OPERATIONS:
• I/O operation means read or write operation with any file or
any specific I/O device.
• Operating system provides the access to the required I/O
device when required.

15. FILE SYSTEM MANIPULATION:
• Program needs to read a file or write a file.
• The operating system gives the permission to the program for
operation on file.
• Permission varies from read-only, read-write, denied, and so
on.
• Operating System provides an interface to the user to
create/delete files.
• Operating System provides an interface to the user to
create/delete directories.
• Operating System provides an interface to create the backup

16. COMMUNICATION:
Following are the major activities of an operating system with
respect to communication:
• Two processes often require data to be transferred between
them.
• Both the processes can be on one computer or on different
computers, but are connected through a computer network.
• Communication may be implemented by two methods, either
by Shared Memory or by Message Passing.

17. ERROR DETECTION:
• The OS constantly checks for possible errors.
• The OS takes an appropriate action to ensure correct and
consistent computing.

18. RESOURCE ALLOCATION
• The OS manages all kinds of resources using schedulers.
• CPU scheduling algorithms are used for better utilization of
CPU.

19. PROTECTION:
• The OS ensures that all access to system resources is
controlled.
• The OS ensures that external I/O devices are protected from
invalid access attempts.
• The OS provides authentication features for each user by
means of passwords.

20. ADVANTAGES OF O S :
• Direct hardware access.
• Fast in speed because it provides direct access of computer
hardware.
• Easy and complete memory use and
• Efficiency use of computer hardware

21. DISADVANTAGES OF O S:
• No back-up available.
• Unrestricted access.
• Deadlock problems
• Problems of memory data loss.

24. 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 . The problems with Batch Systems are as follows:
• Lack of interaction between the user and the job.
• CPU is often idle, because the speed of the mechanical I/O devices
is slower than the CPU.
• Difficult to provide the desired priority.

25. MULTIPROGRAMMING:
• Sharing the processor, when two or more programs reside in memory
at the same time, is referred as multiprogramming.
Multiprogramming assumes a single shared processor .
Multiprogramming increases CPU utilization by organizing jobs so
that the CPU always has one to execute.
• An OS does the following activities related to multiprogramming:
• The operating system keeps several jobs in memory at a time.
• This set of jobs is a subset of the jobs kept in the job pool.
• The operating system picks and begins to execute one of the jobs
in the memory.
• Multiprogramming operating systems monitor the state of all active
programs and system resources using memory management

27. MULTIPROCESSING SYSTEM:
• It allows running a program on more than one CPU
simultaneously . This system is similar to multiprogramming
system , except that there is more than one CPU available.
• In most multiprocessor systems , the processors share a
common memory . Thus the user can view the system as if it
was a powerful single processor.
• Examples: linux , unix and windows.

28. MULTITHREADING:
• Multithreading is a technique in which a process executing an
application is divided into threads that can run concurrently.
• Thread: A dispatchable unit of work. A thread executes
sequentially and is interruptable so that the processor can turn
to another thread.
• Process: A collection of one or more threads and associated
system resources.

29. MULTITASKING OR TIMESHARING:
• Time sharing or Multi tasking is a logical Extension of
multiprogramming. Multiple jobs are executed by the CPU
switching between them , but the switches occur so frequently
that the users may interact with each program while running.
• Time sharing systems were developed to provide interactive
use of a computer at reasonable cost.

30. DISTRIBUTED SYSTEMS:
• A distributed system is a collection of processors that do no
share memory or a clock . Instead each processor has its own
local memory and the processors communicate with each other
through various communication lines.
• The purpose of distributed system is to provide an efficient and
convenient environment for this type of sharing of resources.

31. REAL TIME OPERATING SYSTEM (RTOS):
• Real time operating system are used to control machinery ,
scientific instruments and industrial systems.
• An RTOS typically has very little user interface capability and no
end user utilities, since the system will be a sealed box when
delivered for use.