Thursday, December 23, 2010
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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
- Instructions to Monitor
- Usually denoted by $
- e.g.
- $JOB
- $FTN
- ... Some Fortran instructions
- $LOAD
- $RUN
- ... Some data
- $END
- 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
- I/O devices very slow
- When one program is waiting for I/O, another can use the CPU
- Allow users to interact directly with the computer
- i.e. Interactive
- Multi-programming allows a number of users to interact with the computer
Operating System Support
- Convenience
- Making the computer easier to use
- Efficiency
- Allowing better use of computer resources
- Program creation
- Program execution
- Access to I/O devices
- Controlled access to files
- System access
- Error detection and response
- Accounting
- Interactive
- Batch
- Single program (Uni-programming)
- Multi-programming (Multi-tasking)
- Late 1940s to mid 1950s
- No Operating System
- Programs interact directly with hardware
- Two main problems:
- Scheduling
- Setup time
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