What is Operating System?

Posted by Bhavesh Joshi On Saturday, November 24, 2012 0 comments
Different Operating Systems
Computer hardware provides us the means of processing and storing information. In order to perform useful work for us it has been driven by means of software program which specify the task to be done. Software can be classified into two distinct group - (1) System Software, (2) Application Software. 

System Software- These software's are designed to provide an environment to facilitate the writing of application program. Example-Assemblers, loader, Compiler interpreter, operating system etc. 

Application Software - It consist of collection of program, written by programmer in order to perform some specific task for users. Example - Word Processor, spread sheets, web browser etc.

Definition of Operating System: “Operating system is a system software. It is a collection of program works between the user and hardware of computer. So that application program i.e. user program can run in convenient and efficient manner”. 

Operating system is a chief part of almost every computer system which manages the resources of computer system. Such as microprocessor, primary and secondary storage devices & input/output devices. It keeps the information regarding the status of each resources and decides how long and when to allocate them to specific particular program and users in order to operate the computer system efficiently and fairly. 

Computer system is divided into four parts:

(1) Hardware,
(2) Operating System,
(3) Application Software and
(4) Users 

Computer System Parts

There are two main goals of operating system -

1.       Convenience - The primary goals of operating system is to make computer system easier for user i.e. operating system makes the interaction between user and hardware easier.

2.      Efficient - The secondary goal of OS is to allocate the system resources to various application programs as efficiently as possible. 

Functions of Operating System 

1. Processor management, that is, allocation of processors to different works being done by the computer system. 

2. Memory management, that is, assignment of main memory and other storage areas to the system programs, user programs and data. 

3. Input/Output management, that is, proper interaction and allocation of the various input and output devices when different programs are being executed. 

4. File management, that is, keeping record of files on various storage devices and move all these files from one device to another. It provides facility to all files to be easily changed by the use of text editors. 

5. Give emphasis on building a job priority system. That is, it finds out and keeps record of order in which jobs are to be executed in the computer system. 

6. Switching from job to job as guided by special control statements, automatically. 

7. Understand the meaning of commands and instructions. 

8. Making interfacing and allocation of compilers, assemblers, utility programs, etc to the various users of the computer system. 

9. Building mechanism of data security and integrity. That is, it stores different programs and data in a way that they do not communicate with each other and also protects itself from being damaged by any other user. 

10. Generation of traces, error messages, and other debugging and error-detecting facility. 

11. For all users keep record of internal time clock and log of system usage. 

12. Help easy interfacing between the computer system and the human operator. 

Efficiency of Operating System 

The efficiency of an operating system and the overall performance of a computer installation are judged by a combination of two main factors. They are: 

1. Throughput - It is the total amount of work performed by the computer system over a given duration of time. 

2. Turnaround Time - It is also known as response time and is defined as the difference of time between the time a user submits his job to the system for processing and the time he receives output. 

Ways to interact with Operating System (OS)

1.       By means of operating system call in a program.
2.      Directly by means of Operating System Commands.

System Call

System call provides mechanism for communication between the operating system and user program (processes). The set of system call vary from different operating system. Initially, system calls are written as assembly language instruction. But at present, these are available as high level languages such as 'C, Pascal etc. System calls are classified into five categories- 

1. Process management system call.
2. File management system call.
3. Device management system call.
4. Information management system call.
5. Communication system call.

Types of System Calls and their respective operation

i) Process control system call
(a) end, abort
(b) load, execute
(c) create process, terminate process
(d) get process attributes, set process attributes
(e) wait for time
(f) wait event, signal event
(g) allocate and free memory 

ii) File management system call
(a) Create file, delete file
(b) open, close
(c) read, write, reposition
(d) get file attributes, set file attributes

iii) Device management system call
(a) request device, release device
(b) read, write, reposition
(c) get device attributes, set device attributes
(d) logically attach or detach devices

iv) Information maintenance system call
(a) get time or date, set time or date
(b) get system data, set system data
(c) get process, file, or device attributes
(d) set process, file, or device attributes 

v) Communications system call
(a) create, delete communication connection
(b) send, receive massages
(c) transfer status information
(d) attach or detach remote devices

System Commands
The second way to interact directly with the operating system is with the help of commands. As type commands in MS DOS (Microsoft Disk Operating System) Command Prompt in order interact with the OS directly. There are various commands as each has different use. To know more about command prompt and to get list of commands of windows OS commands– Just Click here!


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