Cpu burst one unit io burst one unit p1 p2 figure 23

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Unformatted text preview: sed. CPU Burst One unit I/O Burst One unit P1 P2 Figure 2.3 Illustration of the multiprogramming concept All jobs that enter the system are kept in the job pool. This pool consists of all processes residing on disk awaiting allocation of main memory. If several jobs are ready to be brought into memory, and there is not enough room for all of them, then the system must choose among them. This decision is called job scheduling. In addition if several jobs are ready to run at the same time, the system must choose among them. We will discuss CPU scheduling in Chapter 6. Time-sharing systems A time-sharing system is multi- user, multi-process, and interactive system. This means that it allows multiple users to use the computer simultaneously. A user can run one or more processes at the same time and interact with his/her processes. A time-shared system uses multiprogramming and CPU scheduling to provide each user with a small portion of a time-shared computer. Each user has at least one separate program in memory. To obtain a reasonable response time, jobs may have to be swapped in and out of main memory. UNIX, Linux, Widows NT server, and Windows 2000 server are timesharing systems. We will discuss various elements of time-sharing systems throughout the course. Real time systems Real time systems are used when rigid time requirements are placed on the operation of a processor or the flow of data; thus it is often used as a control device in a dedicated application. E...
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