Problem Need to distinguish job from job and data from program

Problem need to distinguish job from job and data

This preview shows page 15 - 23 out of 27 pages.

ִ Problem Need to distinguish job from job and data from program.
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Supervisor/Operator Control ִ Secure monitor that controls job processing Special cards indicate what to do. User program prevented from performing I/O ִ Separate user from computer User submits card deck Principles of Operating Systems - Lecture 1 16 cards put on tape tape processed by operator output written to tape tape printed on printer ִ Problems: Long turnaround time - up to 2 DAYS!!! Low CPU utilization I/O and CPU could not overlap. slow mechanical devices.
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Batch Systems - Issues ִ Solutions to speed up I/O: ִ Offline Processing load jobs into memory from tapes, card reading and line printing are done offline. ִ Spooling Use disk (random access device) as large storage for reading as many input Principles of Operating Systems - Lecture 1 17 files as possible and storing output files until output devices are ready to accept them. Allows overlap - I/O of one job with computation of another. Introduces notion of a job pool that allows OS choose next job to run so as to increase CPU utilization.
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Speeding up I/O Principles of Operating Systems - Lecture 1 18
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Batch Systems - I/O completion ° How do we know that I/O is complete? ִ Polling: Device sets a flag when it is busy. Program tests the flag in a loop waiting for completion of I/O. Principles of Operating Systems - Lecture 1 19 ִ Interrupts: On completion of I/O, device forces CPU to jump to a specific instruction address that contains the interrupt service routine. After the interrupt has been processed, CPU returns to code it was executing prior to servicing the interrupt.
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Multiprogramming ° Use interrupts to run multiple programs simultaneously When a program performs I/O, instead of polling, execute another program till interrupt is received. ° Requires secure memory, I/O for each program. Principles of Operating Systems - Lecture 1 20 ° Requires intervention if program loops indefinitely. ° Requires CPU scheduling to choose the next job to run.
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Timesharing ° Programs queued for execution in FIFO order. ° Like multiprogramming, but timer device interrupts after a quantum (timeslice). Interrupted program is returned to end of FIFO Principles of Operating Systems - Lecture 1 21 Next program is taken from head of FIFO ° Control card interpreter replaced by command language interpreter.
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Timesharing (cont.) ° Interactive (action/response) ִ when OS finishes execution of one command, it seeks the next control statement from user.
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