Operating System

Introduction to OS

Operating system is an organized set or collection of software program that controls overall function of the computer system. It is the bridge between the user and computer. OS is also described as "the program which is being initially loaded into the computer and controls the execution of the computer program as well as instructions"

Basic organization of OS

Evolution of OS:

Early computer system used one program at a time, thus the computer operator have to set a particular time manually. She/he has to setup and initiate the processing of the job. These actions is basically flipping a few switches, manually feeding few instructions into the memory etc, which obviously seems very hard job. Therefore in order to over come with all these difficulties OS is developed.

The basic problems associated with early computer system are:

1.     Set up time: How much time the instruction or the program will take to complete it stacks totally. It includes changing tape reel on the tape units, or printer etc.

2.     Manual intervention: This was necessary in order to investigate the error condition and to initiate corrective action. Again the machine will lie idle while this was being done.

3.     Imbalance between processors and peripherals: this meant that the central processor was lying idle for long period of time during the operation of peripheral units.

Functions of OS

·        It manages the sharing of the internal memory among multiple applications.

·        It handles input and output to and from attached hardware devices such as hard disks, printers etc.

·        It sends messages to the applications or interactive users about the status of the operations and any error encountered while performing any tasks.

To the point of the OS can be functioned as:

1.     Memory management: the main function associated with the OS is to manage the memory available to it and its application. Memory is a large group of words, each with its own address. CPU reads from and writes to the specific memory addresses. When the users request the program to run, the OS first determines the amount of memory space required for the program instructions and data. The OS then allocates the amount of memory required and loads the program into RAM. When the program terminates, its memory space is declared free and the same memory area is allocated for the other program.

2.     File input output management: One of the most important components of OS is its file system, which is the part responsible for managing file stored in the hard disk and other mass storage devices. OS provides functions that applications can call to create files, open files for reading and writing, transfer data to and from the file and also perform file management such as renaming, deleting, copying file.

3.     Device I/O management: Device is a hardware such as keyboard, mouse etc. To talk to the device, any of the programs must know the language of the device, which is usually 0s and 1s. Operating system does the function of interpreter.

4.     CPU management: OS handles the problem for assigning the various jobs for processing. The OS helps CPU to schedule its activities so as to meet the demands of various parts of CPU and the computer itself. CPU gets the job from keyboard or storage medium and puts it into the memory, processes the job and passes the result onto the predetermined place and makes itself ready for the next job.

5.     Processor Management: OS assigns different tasks to the processors and manages it in the scheduled way.

Types of OS

We can classify OS as:

1.     Single User OS

              It has the provision to work with only one user. DOS is an example.

2.     Multi User OS

              It has the provision to work with more than one user. Here the total time is divided into time slices and schedule has been made as priority basis. Windows NT, UNIX is an example.

3.     Multitasking

              Here more than one tasks is done in the same time

4.     Multiprocessing

              It is one in which more than one processor are linked together. They share main memory and input/ output device. These processors can execute different independent packages simultaneously.

5.     Real time

              Real time OS are online systems that respond to input immediately. This OS are designed for the purpose of controlling and monitoring external activities with time schedule.

Methods of Operation and Modes of Access:

1.     Multiprocessing

2.     Multiprogramming

3.     Batch processing: It is one of the oldest methods of running program that is still being employed by many data processing centers for processing their jobs. In a batch mode, each user prepares their program offline and submits it to the computer centers. The computer operator puts the entire program in the stack. When a batch of programs has been collected, the operator loads these programs into the computer one after another. This reduces the idle time of the computer system. 

4.     Remote job entry: It refers to the batch processing where jobs are entered from one remote computer and transmitted to the other computer.

5.     Interactive computing: This occurs if the computer and the terminal users can communicate with each other.

6.    Conversational mode: This is interactive computer operation where the response to the user's message is immediate.

7.     Multi access: This occurs if the computer allows interactive facilities to more than one user at a time.

8.     Time-sharing: The processor time is divid0+ed into small units called time slices and shared in turn between users to provide multi access.

9.     Real time system: A real time system is a computer system that is capable of processing data so quickly that the results are available to influence the activity currently taking place. This is an application that requires an immediate response from the computer.

10. Online processing: also called direct access which permits transaction data to be fed under CPU control directly into secondary on line storage devices from the point where data originates without first being stored.

Booting: - When a user switches on the computer, OS conduct a process to load systems files into memory of the computer is called booting. When booting is complete then windows will create user environment (you will see mouse pointer, desktop, icons and taskbar etc.)

There are three essential system files to boot the computer:

1.     IO.SYS

2.     MSDOS.SYS

3.     COMMAND.COM

There are two types of booting

1.     Cold Booting: - First time starting the computer by pressing power button.

2.     Warm Booting: - Restarting the computer by pressing reset button or restarting the computer from shut down or pressing Alt + Ctrl + Delete key

Utility Software

An Utility software is software, which is used for the maintenance purpose or it provides service of developing, editing, debugging & documenting computer programs. They are also known as Service Programs. Some popular utility software are:

1.     Norton Anti-Virus Utility: It protects our computer from Virus attack, we can scan computer to check virus infected and can be removed virus from the computer.

2.     PC Tools: It is used for computer maintenance purpose like cleaning disk or removing unwanted or temp files from the computer etc.

3.     Data recovery:  It is used to recover data from the disk if disk failed or damaged.

4.     Nero-burning Express: It is used to create new CD or to write data in the CD ROM.

These are the few examples of utility software