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Chapter 8: Operating System Support

Chapter 8: Operating System Support. CS 147 Fall 2010 Lester Tam. What is an OS (Operating System)?. Program that manages the computer’s resources Provides services for programmers Schedules the execution of other programs. Types of OS. Interactive or batch?

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Chapter 8: Operating System Support

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  1. Chapter 8: Operating System Support CS 147 Fall 2010 Lester Tam

  2. What is an OS (Operating System)? • Program that manages the computer’s resources • Provides services for programmers • Schedules the execution of other programs

  3. Types of OS • Interactive or batch? • Interactive: Direct communication • Batch: Queued programs • Multiprogramming or uniprogramming? • Multiprogramming: Keep the OS as busy as possible • Uniprogramming: One at a time

  4. Scheduling • Four types of scheduling • Long-term scheduling • Medium-term scheduling • Short-term scheduling • I/O scheduling

  5. Five State Model Process • Used by the short-term scheduler • New • Ready • Running • Waiting • Halted

  6. Process Control Block • Information kept by OS on every process • Identifier • State • Priority • Program counter • Memory pointers • Context data • I/O status information • Accounting information

  7. Memory Management • Swapping • Processes are swapped into Intermediate queue • Partitioning • Fixed-sized partitions • Variable-size partitions

  8. Compaction • Even with dynamic partitioning, memory will become fragmented • The OS will need to “defrag” the memory occasionally • Time consuming • Process may shift in main memory

  9. Paging • Suppose memory is divided into small equal fixed-size chunks (frames) • Same for processes (pages) • Wasted space in memory a fraction of variable partitioning

  10. Virtual Memory • Demand paging – brought in when needed (on demand) • At any time, only a few pages are loaded • Time saved by not having to swap • However, can lead to thrashing • Lead to development of complex algorithms to try to prevent it.

  11. Questions?

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