Although commonly associated with multiprogramming, multiuser OS does not imply multitasking. A multiuser system usually breaks the disk space up into user directories, so that each user has his data files in a separate place (Baldwin 1986, p. 271). Background Processing In a multiuser operating system, two or more active processes are permits. During the execution of such processes, the OS protects the memory space reserved for one process from other processes. Out of multiple processes, most of these systems only process and recognize input from mouse, keyboard, or other input devices (Yadav 2010, p. 146).
This process is known as the foreground processes. The rest of the processes are said to be background processes. Background processes cannot accept interactive participation from a user, but they can access information stored on a disk, ready to write it to the video display. In a large multiuser OS, the number may be hundreds of processes running, with each having several active services at once. In fact, even though no users use the system that is running, dozens of background processes, called daemons (Liu, Yue, & Guo 2011, p.
82), are executing. Types of multi-user operating system Multi-processor There are many types of multiuser operating systems, which work in different ways, intended for completely different purposes. One of these is the multiprocessing system. This is one that executes many processes concurrently. In a unit-process system, when the lone system executes a wait operation, the processor would sit idle and waste time until the process comes out of the wait state. The objective of multiprocessing is to have a process running on the processor at all times (Haldar & Aravind 2010, p. 82).
Multiprocessing can be done in two ways called asymmetric and symmetric multiprocessing. In asymmetric multiprocessing, different jobs may be allocated to different processors. The disadvantage of asymmetric multi-processing is that some processors may be overloaded while other processors remain idle (World 1990, p. 84). In symmetric multiprocessing, the same job may be executed simultaneously at different processors. Time-sliced In a time-sharing system, several users can share the computer resources concurrently. Given that each action and command in a time-shared system takes an extremely minute fraction of time, only a tiny CPU time is desired for each user.
As the CPU toggles rapidly from one user to another, each gets the notion that he has his own computer, while in actuality it is one computer being shared among many users.
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