Operating system (OPS)

An Operating System (OS) is an interface between computer user, computer hardware and computer software.
An operating system is 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, and XP.

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.

Functions of operating systems

 Memory Management
 Processor Management
 Device Management
 File Management
 Security
 Control over system performance
 Job accounting
 Error detecting aids
 Coordination between other software and users. etc.

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 accessed directly by the CPU. For a program to be executed,
it must in the main memory. An 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 parts are not in use?
 In multiprogramming, the OS decides which process will get memory when and how much.
 Allocates the memory when a process requests it to do so.
 De-allocates the memory when a process no longer needs it or has been terminated.

Processor Management

In multiprogramming environment, the OS decides which process gets the processor when and for how much
time. This function is called process scheduling. An Operating System does the following activities for
processor management:

 Keeps tracks of processor and status of process. The program responsible for this task is known as
traffic controller.
 Allocates the processor (CPU) to a process.
 De-allocates processor when a process is no longer required.

Device Management

An Operating System manages device communication via their respective drivers. It does the following
activities for device management:
  Keeps tracks of all devices. The 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 most 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.

An 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 an Operating System performs:

 Security By means of password and similar other techniques, it prevents 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 systems

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.

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 Multiprogrammed Batch Systems and Time-Sharing Systems is that in case of
multiprogrammed batch systems, the objective is to maximize processor use, whereas in Time-Sharing
Systems, the objective is to minimize response time.

Advantages of Times-haring operating systems are as follows:

 provides the advantage of quick response

 Avoids duplication of software
 Reduces CPU idle time

Disadvantages of Time-sharing operating systems are as follows:

 Problem of reliability
 Question of security and integrity of user programs and data
 Problem of data communication

Distributed Operating System

Distributed systems use multiple central processors to serve multiple real-time applications and multiple users.
Data processing jobs are distributed among the processors accordingly. 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.

The advantages of distributed systems are as follows:

 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.

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), and a private network or to other networks.

Examples of network operating systems include Microsoft Windows Server 2003, Microsoft Windows Server
2008, and Linux.

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.
 Remote access to servers is possible from different locations and types of systems.

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.

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.

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 and the data is stored in ROM. In these systems, virtual memory is almost never
found.

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 realities, Advanced Scientific Projects like undersea exploration and planetary rovers, etc.

An Operating System provides services to both the users and to the programs.

 It provides programs an environment to execute.

 It provides users the services to execute the programs in a convenient manner.

Following are a few common services provided by an operating system:

 Program execution
 I/O operations
 File System manipulation
 Communication
 Error Detection
 Resource Allocation
 Protection

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.

A process includes the complete execution context (code to execute, data to manipulate, registers, OS
resources in use). Following are the major activities of an operating system with respect to program
management:

 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

I/O Operation

An I/O subsystem comprises of I/O devices and their corresponding driver software. Drivers hide the
peculiarities of specific hardware devices from the users.

An Operating System manages the communication between user and device drivers.

 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.

File System Manipulation

A file represents a collection of related information. Computers can store files on the disk (secondary storage),
for long-term storage purpose. Examples of storage media include magnetic tape, magnetic disk and optical
disk drives like CD, DVD. Each of these media has its own properties like speed, capacity, and data transfer
rate and data access methods.

A file system is normally organized into directories for easy navigation and usage. These directories may
contain files and other directions. Following are the major activities of an operating system with respect to file
management:

 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 of file system.

Communication

In case of distributed systems which are a collection of processors that do not share memory, peripheral
devices, or a clock, the operating system manages communications between all the processes. Multiple
processes communicate with one another through communication lines in the network.

The OS handles routing and connection strategies, and the problems of contention and security. 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.

Error Handling

Errors can occur anytime and anywhere. An error may occur in CPU, in I/O devices or in the memory
hardware. Following are the major activities of an operating system with respect to error handling:
  The OS constantly checks for possible errors.
 The OS takes an appropriate action to ensure correct and consistent computing.

Resource Management

In case of multi-user or multi-tasking environment, resources such as main memory, CPU cycles and files
storage are to be allocated to each user or job. Following are the major activities of an operating system with
respect to resource management:

 The OS manages all kinds of resources using schedulers.

 CPU scheduling algorithms are used for better utilization of CPU.

Protection

Considering a computer system having multiple users and concurrent execution of multiple processes, the
various processes must be protected from each other's activities.

Protection refers to a mechanism or a way to control the access of programs, processes, or users to the
resources defined by a computer system. Following are the major activities of an operating system with
respect to 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.