Monday, December 20, 2010

Operating System Support - Part 2

Simple Batch Systems
  • Resident Monitor program 
  • Users submit jobs to operator 
  • Operator batches jobs 
  • Monitor controls sequence of events to process batch 
  • When one job is finished, control returns to Monitor which reads next job 
  • Monitor handles scheduling
Job Control Language
  • Instructions to Monitor 
  • Usually denoted by $ 
  • e.g. 
    • $JOB 
    • $FTN 
    • ... Some Fortran instructions 
    • $LOAD 
    • $RUN 
    • ... Some data 
    • $END
Desirable Hardware Features
  • Memory protection 
    • To protect the Monitor 
  • Timer 
    • To prevent a job monopolizing the system 
  • Privileged instructions 
    • Only executed by Monitor 
    • e.g. I/O 
  • Interrupts 
    • Allows for relinquishing and regaining control
Multi-programmed Batch Systems
  • I/O devices very slow
  • When one program is waiting for I/O, another can use the CPU
Time Sharing Systems
  • Allow users to interact directly with the computer 
    • i.e. Interactive 
  • Multi-programming allows a number of users to interact with the computer

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