OPERATING SYSTEM

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Introduction

         It is the software that provide an interface between the computer hardware, and the application program or user. An operating system(OS is the software that provide an interface between the computer hardware, and the application program of the users.

An OS provide standard service(an interface) which are implemented on the hardware, including processes.CPU scheduling, memory management, file system, networking.

Ø  An operating system is a program that acts as an intermediary between a user of a computer and the computer hardware.

Ø  The purpose of an operating system is to provide an environment in which the user can execute program.

The primary goal of operating system is thus to make the computer system convenient to user.

Ø  A secondary goal is to use the computer hardware in an effective manure.

Ø  In brief, an operating system is the set of program that control a computer. Some example of Operating system are UNIX, Mach, MS-DOS,MS Window/NT,OS/2 and Mac OS.

Ø  An operating system is an important part of almost every computer system. A computer system can be divided roughly into four component: the hardware, the operating system, the application system program and the users.

Objective of Operating System

Ø  To hide detail of the hardware by creating abstraction.

Ø  Manage access to shared hardware resources by creating arbitration.

Ø  To allocate resources to process(Manage resources).

Ø  Provide a pleasant and effective and effective user interface.

Feature/Function of Operating System

1.      Process Management                               5.  File System Management

2.      Memory Management                              6.  System Calls and System Programs

3.      File Management

4.      I/O System Management

5.      Networking

6.      Protect System

7.      Command Interpreter System

8.      Program Execution

1.      Process Management

A process is only one instant of  a program in execution. There are many process can be running the same program. The five major activities of an operating system in regard to process management are:

·         Creation and deleting of user and system processes.

·         Suspension and resumption of processes.

·         A mechanism for process synchronization.

·         A mechanism for process communication.

·         A mechanism for deadlock handling.

2.      Memory Management

      Memory is a large array of word or bytes. Each word or byte has its own address. Memory is a repository of quickly accessible data shared by the CPU and I/O devices.

The major activities of an operating system in regard to memory-management are:

·         Keeps tricks of which part of memory are currently being used and by whom.

·         Decide which processes are located into memory space become available.

·         Allocate and deal locate memory space as needed.

3.      File Management

A file is a collection of related information defined by its creator. Computer can store files on the disk(secondary storage), which provide long term storage.

·         The creation and deleting of files.

·         The creation and deleting of directions.

·         The support of primitive for manipulating files and direction.

·         The backup of file on stable media.

·         The mapping of files on the secondary storage.

4.      I/O System Management

One of the purpose of an operating system is to hide the peculiarities of specific hardware devices for the user. A running program may required I/O. This I/O may involve a file or an I/O device.

5.      Secondary Storage Management

Generally speaking, system have several level of storage, including primary storage, secondary storage and cache storage. Instruction and data must be pieced in primary storage or cache to be referenced by a running program.

6.      Networking

A  distribution system is a collection of processes that do not share memory, peripheral devices or a clock. The processors communicate with one another through communication line called networking.

7.      Protection System

Protection refers to mechanism for controlling the access of program, processes or users to the resources defined by a computer system.

8.      Communication System

A communication interpretation is an interface of the operating system with the user. The user gives command with are executed by operating system(usually by turning them into calls).

9.      Program Execution

The system most be able to load a program into memory and to run it. The program most be able to end its execution, either normally or abnormally(indicating errors).

10.   CPU Scheduling

·         CPU or processor is one of the primary computer resources. All computer resources like I/O, memory and CPU scheduling for user.

·         CPU scheduling is important  for operating system. In a multiprogramming and time shearing system, the processor execute multiple processes by switching the CPU among the processes, so that no user has to wait for long for program to execute. To enable running of services concurring processes, the processor time has to be distributed among all the processes  effectively.

·         Scheduler is a component of the operating system that is responsible for scheduling transition of processes. At any one time, only one process can be in running  state and the rest are manually so that no one process is kept waiting for long.

·         Scheduling can be non-pre-emptive scheduling or pre-emptive scheduling. In non-pre-emptive scheduling, the processes executive a process till termination without any interruption. Hence the system resources are not used efficiently. In pre-emptive scheduling a running process may be interrupted by another process that need to executive . Pre-emption allow the operating system to interrupt the executive task and handle any important task that require immediate action. In pre-emptive scheduling, the system resources are used sufficiently.

Types of Operating System:

1.      Single User

Single user operating system can be split into two types:

·         Single user, single application operating system

·         Single user, multi tasking operating system

a)      Single user, single application

This type of operating system only has to deal with one person st time, running one user application at a time. An example of this kind of operating system would be found on a mobile phone. There can only be one user using the mobile and that person is only using od itd application at a time.

b)     Single user, multi-tasking

You will find this kind of operating system on personal computer. The operating system is designed mainly with a single user in mind, but if can be deal with many application running at the same time. For example, you might be writing an essay, while searching the internet, downloading a video file and listening to a piece of music.

Example operating system are: Windows, Linux, Mac OS X

2.      Multi-user

A multi user operating system allow multi user to access a computer system at the same time. Time –sharing system and Internet service can be classified as multi-user system as they enable multiple-user access to a computer through the sharing of time . Single –user operating system have only one user but many allow multi program to run the same time.

3.      Network Operating System

It refers to the software that implement an operating system of same kind that is oriented to computer networking. For example, one that run on a service and enable the service to manage data, user, groups, security, application and other networking function. The networking operating system is designed  to allow shared file and printing access multiple computer in a network, typically a local area network(LAN), a private network or to other networking.

4.      Real-time

A real time operating system is a multitasking operating system that aims at executing real-time application. Real-time operating system often use specialized scheduling algorithms so that can achieve a determination nature of behavior. The main objective of real-time operating system is their quick and predictable response to events. They have an event-driven or tine-shearing design and often aspects of both. An events-driven system switches between tasks beside on their priorities

5.      Multi-tasking vs Single-tasking

A multi-tasking operating system allow more than one program to be running at the same time, for ht e point of view of human time scales. A single tasking system has only one running program. Multi-tasking can be of two types: pre-emptive and co-operation. In pre-emption multitasking, the operating system slices the CPU time and dedication one slot to each of the program. Unis-like operating system such as Solaris and Linux support pre-emption multitasking, as does Amigos Cooperation multitasking is achieved by relaying on each process to the other processes in a defined manure. 16-bit version of Microsoft Word use cooperation multi-tasking . 32-bit version of both Window NT and Win9x used pre-emption multi-tasking. Mac OS TO os x used to support cooperative multitasking.

6.      Distributed

A distributed operating system manage a group of independent computer and makes them appear to be single computer. The development of networking computer that could be linked and communicate with each other gave rise to distributed computer. Distributed computer are carried out on more than one machine. When computer in a group work in cooptation, they make a distributed system.

7.      Embedded

Embedded operating system are designed to be used in embedded computer system. They are designed to operate on small machine like PDAs with less autonomy. They are able to operate with a limited number of resources. They are very compact and extremely efficient by design. Window CE and Minx 3 are the example of embedded operating system.

8.      Batch processing

It is the execution of a series of program(job) on a computer without manual intervention. It is often not desirable to deal with the input units a certain number have occurred or a set time has passed. So they are stored until the system come to process the data in one batch has passed. It queues up program so that as soon as one program completed the next would start.

Open Source Operating System

Normally, software is distributed in the market in the form of executive binary files. The user of the software cannot modify it, as source code of the program is not proved. The open source software came with a different concept. Along with executable binary files, source code is also supplied to the user that sophisticated users or programmer can modify their code as per their requirement. All the open source software is not free. The open source operating system Linux as free but UNIX is not free. We are going to discuss two open spruce operating system Linux and UNIX only.