6 multiprogramming & time sharing
- 1. Basics of Operating Systems : Multiprogramming & Time Sharing 1
- 2. Recap In the last class, you have learnt about • Spooling • Buffering 2
- 3. Objectives On completion of this period, you would be able to know • Multiprogramming • Time Sharing 3
- 4. Multiprogramming • A program under execution is called a process • Serial execution of the program causes either the process or I/O devices to be ideal at some time even if the input job stream is never empty – a problem ( refer next slide ) • Solution to this problem is to assign some other work to the processor and I/O devices when they are idle • Allow programs to execute concurrently by assigning pending work to under utilized components 4
- 5. Example Program 1 Program 2 P1 IDLE P1 IDLE P1 P2 IDLE P2 IDLE P2 Time Processor Activity Multi Programming 5
- 6. Multiprogramming • Previous Figure illustrates a possible scenario of concurrent execution of the two programs • It starts with the processor executing the first computational sequence program 1 • Instead of idling during the I/O sequence of program 1, the processor is assigned to the first computation sequence of the program 2, which is assumed to be in memory and awaiting for execution • When this work is done, the processor is assigned to program 1 again, then to program 2, and so forth 6
- 7. Multiprogramming (Contd..) • Performance of processor may be improved by interleaved execution of programs • With a single processor, parallel execution of program is not possible, and at most one program can be in control of the processor at any time 7
- 8. Multiprogramming (Contd..) • It achieves 100% processor utilization with only two active programs • Multiprogramming has been employed to increase resource utilization of a computer system and to support multiple, simultaneously active users 8
- 9. Multiprogramming (Contd..) • Multiprogramming system is provided by time sharing systems found in many university computer centers • Time sharing systems support multiple interactive users • System and user programs, as well as data, are kept on the secondary storage which is managed by the file system 9
- 10. Time sharing • Time sharing is the logical extension of Multiprogramming • Time sharing systems executes multiple jobs by switching among them ( refer next slide ) • Switches occurs frequently so that the user can interact with each program while it is running • Each program executes for a fixed time quantum 10
- 11. Example Program 1 Program 2 P1 P2 P1 P2 P1 P2 Time Time Sharing 11
- 12. Timesharing (Contd..) • 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 the computer simultaneously • Each action or command in a time shared system is short, only a little of CPU time is required for each user 12
- 13. Timesharing (Contd..) • The system switches rapidly from one user to the next • User gets the impression that the entire system is dedicated to his use • Time shared operating system uses CPU scheduling and Multiprogramming to provide • each user with a small portion of a time-shared system 13
- 14. Frequently Asked Questions • Explain Multiprogramming systems • Explain Time Sharing systems 14
- 15. Quiz • Programs are developed and executed in the interactive mode Yes No 15
- 16. Quiz • A program in execution is called process Yes No 16
- 17. Click here to see Operating Systems Basics of Operating Systems Definition of Operating Systems 1.4 Know about concept of spooling and buffering ppt Other subject materials • Web designing • Micro processors • C++ tutorials • java home 17