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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

Chapter 8: Operating System Support

CS 147 Fall 2010

Lester Tam

what is an os operating system
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
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
scheduling
Scheduling
  • Four types of scheduling
    • Long-term scheduling
    • Medium-term scheduling
    • Short-term scheduling
    • I/O scheduling
five state model process
Five State Model Process
  • Used by the short-term scheduler
    • New
    • Ready
    • Running
    • Waiting
    • Halted
process control block
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
memory management
Memory Management
  • Swapping
    • Processes are swapped into Intermediate queue
  • Partitioning
    • Fixed-sized partitions
    • Variable-size partitions
compaction
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
paging
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
virtual memory
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.