An Operating System, or OS, is a software program that enables the computer hardware to communicate and operate with the computer software. Without a computer Operating System, a computer would be useless.
Basic functions of an operating system:- Operating system controls and coordinates the use of the hardware among the various applications programs for various uses.• Operating system acts as resource allocator and manager. Since there are many possibly conflicting requests for resources the operating system must decide which requests are allocated resources to operating the computer system efficiently and fairly?
• Operating system is control program which controls the user programs to prevent errors and improper use of the computer. It is especially concerned with the operation and control of I/O devices.
• Multiprogramming :– In multiprogramming more than one program reside in the main memory. When one job is unable to execute because of I/O operation to complete, it switches to other program and allow that program to run the main motive of multiprogramming is to utilize the CPU efficiently.
• Multitasking:-In multitasking operating system more than one program is assigned to the CPU or switches between the programs occurs so fast that it seems like more than one program is running. The main motive of multitasking is to utilize the CPU efficiently and reduce the response time.
• Multiprocessing-In multiprocessing operating system a task is divided between more than one processor (CPU) so that parallelism can be achieved.
• Multithreading -Sometime a program need to do multiple task at the same time. It is an extension of multiprogramming. In multithreading the program is divided into multiple task. Throughput, Turnaround time, waiting time and Response time -:
• Throughput – number of processes that complete their execution per time unit.
• Turnaround time – amount of time to execute a particular process.
• Waiting time – amount of time a process has been waiting in the ready queue.
• Response time – amount of time it takes from when a request was submitted until the first response is produced, not output (for time- sharing environment). Hard and Soft real-time systems:-
• A hard real time system guarantees that critical tasks complete on time. This goal requires that all delays in the system be bounded from the retrieval of the stored data to the time that it takes the operating system to finish any request made of it.
• A soft real time system where a critical real-time task gets priority over other tasks and retains that priority until it completes. As in hard real time systems kernel delays need to be bounded
• In 1983 Bill Gates announces Microsoft Window November 10, 1983,
• Microsoft Windows 1.01 is introduced in November 20,1985 and initially sold for $100.00
• Microsoft Windows 1.03 is introduced in August 1986.
• Microsoft Windows NT( New Technology) is introduced in 27 July 1993.
• Microsoft Windows ME( Millennium ) is introduced in 2000.
• Microsoft Windows XP (eXPerience ) is introduced in 25 October 2001.