1. Operating system : A BCA notes

 1. Operating system

Introduction

In early day of computer, Computer were very huge and expensive to buy and run. The user at that time interacted directly with the hardware to the machine language. A software was required which could perform basic tasks such as recognizing input from  the keyboard, sending output to the display screen, keeping track of the files and directories stored on magnetic disc and controlling the peripheral devices such as printer and scanner etc. Such software lead to the evolution of modern days operating system (OS). This software is loaded on the above and all the basic task. Initially OS was only character based. This interface provides, the user  with a command, and the user has to type all the commands to perform various function, as a result, User has to memoirs many commands to perform with the complex function. OS become  more user-friendly by providing graphical user interface (GUI). the GUI based OS allows manipulation of software by using various objects such as windows, pull down menu, mouse pointer and icons, consequently the OS become very easier to understand and learn.

Definition

An operating system is a collection of systems programs that together controls computer the operation of a computer system. The OS along with hardware, application and other system software and user constitute a computer system, It is the most important part of the computer system. It acts intermediate between the user and to provide user interactive interface so that commands can be communicated to the hardware.

Types of operating system

The OS have evolved from its primitive days to the era of digital world from batch operating system ; the different types of OS can be classified into six categories.

a.) Batch processing OS

b.) Time sharing / Multi-user OS

c.) Multi tasking OS

d.) Real time OS

e.) Multi processor OS

f.) Embedded OS

Components of OS

The common component of various OS is

(1.) Process management

The OS manage many kind of activity arranging from the users program to the system program. Each of there activities are encapsulated related as a process, a process introduce complete execution contains i.e. code, data, program counter, register OS resources  etc.

    It is important to know that process is not a program; a process is only one instant of a program  in execution. There are many processes that can be running at the same time. The five major activity of as OS is regards to process management are :

a.) Creation and deletion of the user and system process.

b.) Suspension and resumption of process.

c.) A mechanism of process synchronization.

d.) A mechanism of process communication.

e.) A mechanism of deadlock handy.

(2.) Main memory management

Primary memory or main memory is a large array of the world or wide as its own address. Main memory provides storage that can be access directly by the CPU. The major activities of an OS in regards to memory management are :

a.) If track of which part of memory are currently used by whom.

b.) Decides which process is loaded into the memory space become unreliable.

c.) Allocated and delicate memory space as needed.   

(3.) File management

A file is a collection of related information defined by its creator. Computer can store the file on a secondary storage device which provides long term storage. The file system normally organized into directory to ease their use. This directory may contain files and other sub-directories. The five main common activity of an OS in regards to file management are :

a.) The creation and deletion of file.

b.) The creation and deletion of directories.

c.) The support of primitive for manipulating files and directories.

d.) The mapping of files into secondary storage.

e.) Backup of the file on suitable storage media and to restore them.

(4.) Input / Output system management

I/O subsystem files the peculiarities of specific hardware devices from the user only the device driver knows the peculiarities of the specific devices to move it to assign.

(5.) Secondary storage management

Computer system have several levels of storage including  primary storage, secondary storage, cache storage instruction and data must be paste in primary storage or cache to be reffed  by a running program because main memory is too small to access all data to the program. Secondary storage of media or semiconductor to hold information which can be  loaded to primary memory before its execution. The three major activities of OS in regards to secondary memory management are :

a.) Managing the free space available on the secondary storage devices.

b.) Allocation of storage space that new file have to be written.

c.) Scheduling the request for memory access.

(6.) Networking components

A distributed system is a collection of process that do not share memory peripheral devices or a clock. the process or communication with one another though communication network design must consider routing and connection strategy and the problem of contention and security.

(7.) Protection system

If a computer system has multi users and allow the concurrent execution of multiple processes than the various activity. Protection refer to mechanism for controlling the access of program process or users to the resources defined by a computer system.

(8.) Command interpreter system 

It is an interface of an OS with the user. The user gives commands with are executed by OS call. The main function of command interpreter is to get and execute the next user specified command. It is usually not a part of kernal system. Since multiple commands system may be supported by the operating system and they do no really need to run kernal mode.

Services of Operating system

The program execution, input/output operation, five manipulation, communication and error delectation are five services provided by operating system to the convenience of the users.

(1.) Program execution

The purpose of the computers system is to allow the user to execute programs. So the OS provides an environment where the user can conveniently run programs the user does not have to worry about the memory allocation or the multitasking or anything else. These things are taken can by the operating systems.

    Running the program involves allocating and deallocating memory CPU scheduling in case of multiprocessing. These functions cannot be given to the user level program. So user level program cannot help the user to run program independently without the help of OS.

(2.) Input / Output operations

Each program requires an input and produces output. This involves the use of I/O. The OS hides the user the details of underlying hardware for the I/O. All the user make it convenient for the users to run programs.

    For efficiency and protection users cannot control I/O so this services cannot be provided by user-level programs.

(3.) File system manipulation 

The output of a program may need to be written into new files or input take from same files. the OS provide this service. The user does not have to worry about secondary storage management user gives a command for reading or writing to a file and sees his task accomplished.

    Thus, OS makes it easier for user programs to accomplish their task.

    This service involves secondary storage management. The speed of I/O that depends on secondary storage management is critical to the speed of many programs and hence i think it is best relegated to the OS to mange it than giving individual users the control of it. It is not difficult for the user level programs to provide these services but for above mentioned reasons it is best if this services left with OS.

(4.) Communication

There are instances where processes need to communicate with each other to exchange information. It may be between processes running on the same computer or running on the different computer. By providing this service the worry of passing massages between process. In case where the message need to be passed to processes on the other computers through a network it can be done by the user programs. The user promay be customized to the specifics of the hardware through which the message tanis its and provides the service interface to the OS.

(5.) Error detection

An error is one part of the system may cause malfunctioning of the complete system. To avoid such a situation the OS constantly monitors the system for deleting the errors. This relieves the user of the worry of errors propagating to various part of the system and causing malfunctioning.

    This service cannot allowed to be handled by user programs because it involves monitoring and in cases altering area of memory of deallocation of memory for a faulty process, or may be relinquishing the CPU of a process that goes into an infinite loop. These tasks are too critical to be handed over to the user programs. A user program if given these privileges can interface with the correct (normal) operation of the OS.

Operating system for different computers

Operating system can be group together by its functionality i.e. OS for super computer, computer cluster, Mainframe computer, servers, work station, desktop computer, hand held devices, real time system or for embedded system.

(1.) OS for Super computer

Super computer are the fastest computer, very expensive and are embedded for specified application that required amines amount of mathematical calculation. E.g. weather Forecasting, graphics animation, fluid dynamic circularity, nuclear energy research and Petroleum exploration out of many OS for supercomputing, UNIX and Linux are the most dominants ones.

(2.) Computer cluster Operating system

A computer cluster OS is the group of computer system that works together so that in many respect they can be view as single computer system. The components of cluster are commonly connected of cluster are commonly connected to each other through the fast local area network (LAN) beside many open source OS, and they run version of window service 2003, Linux is popularly used computer cluster.

(3.) Mainframe Operating system

Mainframe used to be a primary form OS mainframe is large centralized computer an at a time they provide a bulk of centralized process. Mainframe are still used foe some large still task centralized billing system, inventory system, database system.

(4.) Mini computer

Mini Computer are smaller less expensive version of the mainframe business that could not afford mainframe computer, the chief difference between super computer and mainframe computer is that, a super computer used its power to execute many program consequently, beside various versions of operating system. By IBM for its easily system 360 degree to its newest Z series. UNIX and Linux are also used on mini computer.

(5.) Server Operating system

Server are computer are group of computer that provide services to other computer connection by a network based on the requirement there  are various version of the serve OS from the different vendeor starting with Microsoft server from windows NT to windows 2009 OS, Ubuntu server, UNIX server, Mac OS server and various flavor of Linux servers.

(6.) Work station Operating System

Work Station are more powerful version of personal computer like desktop computer, only one person uses a particular work station and run a more powerful version of desktop OS, most of the time work station used as a clients in network, environment the popular work station are windows NT work station, Window 2000, peripheral OS, Oblique to client, Mac OS, UNIX, Linux etc. .

(7.) Desktop Operating System 

A personal computer is the micro computer whose price size and capability make it useful for individual they are also know as desktop computer or home computer. Desktop OS are used for PC as Mc dos, Windows 9X, Window XP, Window 7, Window 8, Window 10, Mac OS, UNIX, Linux etc. .

(8.) Embedded Operating system 

Embedded systems are combination of processor and special software that are inside of another device such as electronic emissions system in two cars. The example of embedded OS is Linux, Windows CE, RT operation system etc. .

(10.) Operating system for handheld device

Handheld OS are much smaller and less capable than the desktop operating system so that they can be fit into a limited memory of handheld devices. The OS including plan OS, EPOC, dos, android, window CE, Pocket Linux etc. .

Assignment

1. What do the term program process and threads means.

2. What is purpose of translator and how do they work.

3. What is the structure of the code file, what is the purpose of symbol table in the code file?

4. Why are shared libraries essential on  modern computer?

5. Discuss the various components of the OS?

6. Explain memory management and file management in brief.

7. Write a short notes on secondary storage management and command interprets system.

8. Explain the five service provided by O.S.