MultiProgramming
Filed under
by
Nahal Ahmed
on
4:03 PM
A multiprogramming or multitasking OS is a system executing many processes concurrently. Multiprogramming requires that the processor be allocated to each process for a period of time and de-allocated at an appropriate moment. If the processor is de-allocated during the execution of a process, it must be done in such a way that it can be restarted later as easily as possible.
There are two possible ways for an OS to regain control of the processor during a program’s execution in order for the OS to perform de-allocation or allocation:
1. The process issues a system call (sometimes called a software interrupt); for example, an I/O request occurs requesting to access a file on hard disk.
2. A hardware interrupt occurs; for example, a key was pressed on the keyboard, or a timer runs out (used in pre-emptive multitasking).
The stopping of one process and starting (or restarting) of another process is called a context switch or context change. In many modern operating systems, processes can consist of many sub-processes. This introduces the concept of a thread. A thread may be viewed as asub-process; that is, a separate, independent sequence of execution within the code of one process. Threads are becoming increasingly important in the design of distributed and client–server systems and in software run on multi-processor systems.
Comments:
Post a Comment