Multiprogramming&timesharing

1. MULTIPROGRAMMING & TIME SHARING Tanuj Tyagi 091277

2. Multiprogramming Multiprogramming is a technique to execute number of programs simultaneously by a single processor. In Multiprogramming, number of processes reside in main memory at a time. The OS picks and begins to executes one of the jobs in the main memory. If any I/O wait happened in a process, then CPU switches from that job to another job. Hence CPU in not idle at any time.

3. OS Job 1 Job 2 Job 3 Job 4 Job 5 Figure dipicts the layout of multiprogramming system. The main memory consists of 5 jobs at a time, the CPU executes one by one.

4. Multiprogramming enables time sharing - divides processor time up into slices - the slices are divided “fairly” among competing jobs interactive processing - the user does not have to wait for one process to be finished until the next process (program, action) can be started

5. Degree of Multiprogramming CPU utilization of a system can be increased by multiprogramming. Let P be the fraction of the time that process spends away from the cpu . If there is one process Cpu utilization time is 1-p.

6. If there is N process then probability of N process waiting for an I/O is P*P*P(N times). Then CPU utilization is 1-P^N, where N is degree of multiprogramming level.

7. Advantages Efficient memory utilization Throughput increases CPU is never idle, so performance increases

8. Time Sharing Time sharing, or multitasking, is a logical extension of multiprogramming. Multiple jobs are executed by switching the CPU between them. In this, the CPU time is shared by different processes, so it is called as “Time sharing Systems”. Time slice is defined by the OS, for sharing CPU time between processes. Example Unix

9. Time Sharing requires an interactive computer system i.e. direct communication between the user and the system. Time Sharing OS allows many users to share computer simultaneously. The system switches rapidly from one user to next.

10. THANK YOU