1. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Chapter 3: Operating Systems Computer Science: An Overview Tenth Edition by J. Glenn Brookshear

2. 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

3. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-3 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

4. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-4 Figure 3.1 Batch processing

5. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-5 Figure 3.2 Interactive processing

6. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-6 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

7. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-7 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

8. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-8 Figure 3.4 The shell as an interface between users and the operating system

9. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-9 File Manager Directory (or Folder): A user-created bundle of files and other directories (subdirectories) Directory Path: A sequence of directories within directories

10. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-10 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:

11. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-11 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

12. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-12 Figure 3.5 The booting process

13. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-13 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

14. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-14 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.

15. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-15 Figure 3.6 Time-sharing between process A and process B