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Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Chapter 3: Operating Systems
Computer Science: An OverviewTenth Edition
by J. Glenn Brookshear
Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-2
Functions of Operating Systems
• Oversee operation of computer• Store and retrieve files• Schedule programs for execution• Coordinate the execution of programs• The best known examples:
– Windows– Unix– Linux
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Evolution of Shared Computing
• The execution of each program is called job.• Batch processing
– Execution of jobs in a single batch, no interaction with user
• Interactive processing– Requires real-time processing– Execution of jobs through dialogue with user via remote terminals
• Time-sharing/Multitasking– Rotate jobs– Implemented by Multiprogramming
• Multiprocessor machines
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Figure 3.1 Batch processing
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Figure 3.2 Interactive processing
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Types of Software
• Application software– Performs specific tasks for
users• System software
– Provides infrastructure for application software
– Consists of operating system and utility software
• Utility Software– Programs for performing
activitis that are fundamental to computer installation but not included in OS.
– Ex: sw to format a disk
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Operating System Components
• Shell: Communicates with users– Text based– Graphical user interface (GUI)
• Kernel: internal part of OS. – File manager: coordinate the machine’s mass storage
facilities– Device drivers: communicate with controllers– Memory manager: coordinate machine use of memory– Scheduler / dispatcher: determines which activities are
to be considered for execution / controls the allocation of time to these activities
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Figure 3.4 The shell as an interface between users and the operating system
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File Manager
• Directory (or Folder): A user-created bundle of files and other directories (subdirectories)
• Directory Path: A sequence of directories within directories
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Memory Manager
• Allocates space in main memory• May create the illusion that the machine
has more memory than it actually does (virtual memory) by playing a “shell game” in which blocks of data (pages) are shifted back and forth between main memory and mass storage
• Ex:
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Getting it Started (Bootstrapping)
• Bootstrap: Program in ROM (example of firmware)– Run by the CPU when power is turned on– Transfers operating system from mass storage
to main memory– Executes jump to operating system
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Figure 3.5 The booting process
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Processes
• Process: The activity of executing a program
• Process State: Current status of the activity– Program counter– General purpose registers– Related portion of main memory
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Process Administration
• Scheduler: Adds new processes to the process table and removes completed processes from the process table
• Dispatcher: Controls the allocation of time slices to the processes in the process table– The end of a time slice is signaled by an
interrupt.
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Figure 3.6 Time-sharing between process A and process B
