Understanding Basics of OS

Presentation Prepared By
V. Backiyalakshmi M.Phil.,NET
Assistant Professor of Computer Science
E.M.G. Yadava Women’s college,
Madurai.

Contents
 Introduction
 Definition
 Memory Management
 Processor Management
 Device Management
 File Management
 Other Important Activities
 Batch operating system
 Time-sharing operating systems
 Distributed operating System
 Network operating System
 Real Time operating System

Introduction
 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.
 An operating System (OS) is an intermediary between users and computer hardware.
 It provides users an environment in which a user can execute programs conveniently
and efficiently.
 In technical terms, It is a software which manages hardware.
 An operating System controls the allocation of resources and services such as
memory, processors, devices and information.

Definition
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.

Important Functions of An Operating System
 Memory Management
 Processor Management
 Device Management
 File Management
 Security
 Control over system performance
 Job accounting
 Error detecting aids
 Coordination between other software and users

Memory Management
 Memory management refers to management of Primary Memory or Main Memory.
Main memory is a large array of words or bytes where each word or byte has its own
address.
 Main memory provides a fast storage that can be access directly by the CPU. So for a
program to be executed, it must in the main memory. Operating System does the
following activities for memory management.
 Keeps tracks of primary memory i.e. what part of it are in use by whom, what part
are not in use.
 In multiprogramming, OS decides which process will get memory when and how
much.
 Allocates the memory when the process requests it to do so.
 De-allocates the memory when the process no longer needs it or has been terminated.

Processor Management
In multiprogramming environment, OS decides which process gets the
processor when and how much time. This function is called process scheduling.
Operating System does the following activities for processor management.
 Keeps tracks of processor and status of process. Program responsible
for this task is known as traffic controller.
 Allocates the processor(CPU) to a process.
 De-allocates processor when processor is no longer required.

Device Management
OS manages device communication via their respective drivers. Operating
System does the following activities for device management.
 Keeps tracks of all devices. Program responsible for this task is known as
the I/O controller.
 Decides which process gets the device when and for how much time.
 Allocates the device in the efficient way.
 De-allocates devices.

File Management
A file system is normally organized into directories for easy navigation
and usage. These directories may contain files and other directions. Operating
System does the following activities for file management.
 Keeps track of information, location, uses, status etc. The collective
facilities are often known as file system.
 Decides who gets the resources.
 Allocates the resources.
 De-allocates the resources.

Other Important Activities
Following are some of the important activities that Operating System does.
Security -- By means of password and similar other techniques, preventing
unauthorized access to programs and data.
Control over system performance -- Recording delays between request for a
service and response from the system.
Job accounting -- Keeping track of time and resources used by various jobs and
users.
Error detecting aids -- Production of dumps, traces, error messages and other
debugging and error detecting aids.
Coordination between other software and users -- Coordination and assignment
of compilers, interpreters, assemblers and other software to the various users of
the computer systems.

Types of Operating System
Operating systems are there from the very first computer generation. Operating systems
keep evolving over the period of time. Following are few of the important types of operating system
which are most commonly used.
 Batch operating system
 Time-sharing operating systems
 Distributed operating System
 Network operating System
 Real Time operating System

Batch operating system
 The users of 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.
 Thus, the programmers left their programs with the operator. The
operator then sorts programs into batches with similar requirements.
The problems with Batch Systems are following.
 Lack of interaction between the user and job.
 CPU is often idle, because the speeds of the mechanical I/O devices is
slower than CPU.
 Difficult to provide the desired priority.

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 main difference between Multi-programmed Batch Systems and Time-
Sharing Systems is that in case of Multi-programmed batch systems,
objective is to maximize processor use, whereas in Time-Sharing Systems
objective is to minimize response time.
 Multiple jobs are executed by the CPU by switching between them, but the
switches occur so frequently.
 Thus, the user can receives an immediate response.

Advantages of Timesharing operating systems are
 Provide advantage of quick response.
 Avoids duplication of software.
 Reduces CPU idle time.
Disadvantages of Timesharing operating systems are
 Problem of reliability.
 Question of security and integrity of user programs and data.
 Problem of data communication.
Time-sharing operating systems cont..

Distributed operating System
 Distributed systems use multiple central processors to serve multiple real time
application and multiple users. Data processing jobs are distributed among the
processors accordingly to which one can perform each job most efficiently.
 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.

Distributed operating System Cont..
The advantages of distributed systems are
 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.

Network operating System
 Network Operating System runs on a server and provides 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.
 Examples of network operating systems are Microsoft Windows Server 2003,
Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell NetWare, and
BSD.

Network operating System Cont..
The advantages of network operating systems are following.
 Centralized servers are highly stable.
 Security is server managed.
 Upgrades to new technologies and hardware can be easily integrated into
the system.
 Remote access to servers is possible from different locations and types of
systems.
The disadvantages of network operating systems are following.
 High cost of buying and running a server.
 Dependency on a central location for most operations.
 Regular maintenance and updates are required.

Real Time operating System
 Real time system is defines 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.
 Real time processing is always on line whereas on line system need not be real time.
 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 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.
Real Time operating System Cont..

Understanding Basics of OS

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