Operating System- Definition and Types
Operating System
An operating system is System Software that utilizes the computer resources effectively and acts as a user interface between user and computer. The main purpose of operating system (OS) is to effectively manage the hardware and software resources of a computer system. System software controls the working of hardware and aids in effective execution of a general user’s applications. Without an operating system, it is not possible to use the computer.
Examples of Operating Systems:-
• Microsoft Windows (OS)
• Mac OS X
• GNU/Linux
• Unix
• Plan 9
Different types of Operating Systems are:
• Batch Processing System
• Multiprogramming operating System
• Time Sharing System
• Real Time Systems
Batch Processing System
The main function of a batch processing system is to automatically keep executing one job to the next job in the batch. The main idea behind a batch processing system is to reduce the interference of the operator during the processing or execution of jobs by the computer. The batch monitor carries out all functions of a batch processing system. The batch monitor permanently resides in the low end of the main store. The current jobs out of the whole batch are executed in the remaining storage area. In other words, a batch monitor is responsible for controlling all the environment of the system operation. The batch monitor accepts batch initiation commands from the operator, processes a job, perform the job of job termination and batch termination. In a batch processing system, we generally make use of the term ‘turn around time’. It is defined as the time from which a user job is given to the time when its output is given back to the user. This time includes the batch formation time, time taken to execute a batch, time taken to print results and the time required to physically sort the printed outputs that belong to different jobs. As the printing and sorting of the results is done for all the jobs of batch together, the turn around time for a job becomes the function of the execution time requirement of all jobs in the batch. You can reduce the turn around time for different jobs by recording the jobs or faster input output media like magnetic tape or disk surfaces. It takes very less time to read a record from these media. For instance, it takes round about five milliseconds for a magnetic ‘tape’ and about one millisecond for a fast fixed-head disk in comparison to a card reader or printer that takes around 50-100 milliseconds. Thus, if you use a disk or tape, it reduces the amount of time the central processor has to wait for an input output operation to finish before resuming processing. This would reduce the time taken to process a job which indirectly would bring down the turn-around times for all the jobs in the batch.
Multiprogramming Operating System
The objective of a multiprogramming operating system is to increase the system utilisation efficiency. The batch processing system tries to reduce the CPU idle time through operator interaction. However, it cannot reduce the idle time due to IO operations. So, when some IO is being performed by the currently executing job of a batch, the CPU sits idle without any work to do. Thus, the multiprogramming operating system tries to eliminate such idle times by providing multiple computational tasks for the CPU to perform. This is achieved by keeping multiple jobs in the main store. So, when the job that is being currently executed on the CPU needs some IO, the CPU passes its requirement over to the IO processor. Till the time the IO operation is being carried out, the CPU is free to carry out some other job. The presence of independent jobs guarantees that the CPU and IO activities are totally independent of each other. However, if it was not so, then it could lead to some erroneous situations leading to some time-dependent errors.
Time Sharing Systems
The time sharing systems were developed with a main aim to provide fast response to the requests made by the user. The computing environment which best illustrates the advantages of time-sharing systems over multiprogramming or batch processing systems is one in which a number of interactive terminals are simultaneously used for program development and computational purposes. The response given by the system is shown visually on the screen. The user expects a very fast response from the system if the request made by him requires very less processing by the CPU. For instance, on giving a program statement by the user, the compiler should display the error message quickly. If this interaction takes little time, then the compilation of the user program will proceed rapidly. Both the interactive as well as non-interactive programs can participate in time-sharing. The time sharing systems provide a good rate of program activity for all programs in the system. In order to provide good program activities, certain basic changes are required in the structure of the operation system. These changes mainly involve the processor management and storage management components of the operating system. Let us discuss them in detail.
Real Time Systems
Since the earliest days of computing, the range and complexity of applications into which computers were drawn has risen to a greater extent. A specific class among these is the real time systems. A real time system is said to be one which responds back fast so that it is able to make an impact on the environment in which it is working. A real time system is actually very fragile because any system interacts with its working environment. The real time system is mostly applied in those systems where the response or the feedback is immediately required. For instance, process control systems in factories or missile tracking system for defence. Another important area of real time system application is in the airline seat reservation system in whose case the availability of a seat is checked, reserved and booked while the operator is interacting with the customer.
Thus, the interaction between the computer and the application environment has to be very quick in case of a real time system. Therefore, the operating system has to be designed in such a manner so that it is able to meet the need of quick response. However, the response requirements of an application are found out by the nature and type of the application. Since the response time requirements of a real time system are critical, a general time sharing system may not be able to satisfy them. When a real time application is to be supported by a computer system along with general time sharing series, then the real time application is given the higher processing priority. This helps in giving out a quick response for the application.
Functions of an Operating System
An operating system must perform at least the following functions in order to enable the computer to process user programs satisfactorily.
• Processor Management is concerned with allocating CPU to various competing jobs/processes to ensure maximum output from the system.
• Input/Output or Device Management refers to coordination and control of various I/O devices and is an important function of the operating system. This involves receiving the request for I/O interrupts and communicating back to the requesting process.
• Memory Management OS allocates memory to itself and its resident system programs, sets aside areas for application program and user partition, arranges the I/O buffers and reserves storage for specialised purposes.
• File Management or Information Management computers use a lot of data/programs which are stored on secondary storage devices. File management function of an OS involves keeping track of all different files and maintaining the integrity of data stored in the files including file directory structure.
• Job Control When the user wants to run an application program, he must communicate with the OS, telling it what to do. He does this by using the OS’s job control language or JCL. JCL consists of a number of OS commands, called system commands, that control the functioning of the operating system.
• House Keeping includes all the support services necessary to ensure smooth operation of the computer system, viz., security, protection, and resource accounting, back-up and restoration, etc.
Popularity: 1% [?]
