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 Chapter 3: Operating Systems 3.1 The History of Operating Systems 3.2 Operating System Architecture 3.3 Coordinating the Machine’s Activities

3. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-3 Functions of Operating Systems Coordinate a computer’s internal activities –Schedule programs for execution –Coordinate the execution of programs –Store and retrieve files – etc.. Oversee operation of computer with outside world

4. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Examples of Operating Systems Windows (Microsoft) UNIX Mac OS Solaris Linux 3-4

5. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-5 Evolution of Shared Computing 1.Batch processing –No interaction during the execution of programs 2.Interactive processing –Requires real-time processing 3.Time-sharing/Multitasking –Implemented by Multiprogramming 4.Multiprocessor machines

6. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-6 Figure 3.1 Batch processing No interaction during the execution of programs Computer operator Job queues ( FIFO, Priority)

7. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-7 Figure 3.2 Interactive processing Interaction by real time processing What happens if there are several users?

8. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Time-sharing/Multitasking Multiple users  Time sharing Time sharing may be implemented by multiprogramming (divide time into intervals) Time sharing systems enable acceptable real-time processing to as many as 30 users simultaneously 3-8

9. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Time-sharing/Multitasking Multitasking: One user executes numerous tasks simultaneously Multi processor systems provide time- sharing/multitasking by assigning different tasks to different processors –Load balancing (Efficient usage of processors) –Scaling (Breaking tasks into several pieces to assign them in different processors) 3-9

10. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-10 Types of Software Application software –Performs specific tasks for users –Examples: Spreadsheets, Word Processors, Database systems, etc. System software –Provides infrastructure for application software –Two categories of system software: –operating system (OS) –utility software (such as software to format a magnetic disk, to compress/decompress data; disk fragmenters, screen savers, etc.)

11. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-11 Figure 3.3 Software classification

12. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-12 Figure 3.4 The shell as an interface between users and the operating system

13. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-13 Operating System Components Shell: Communicates with users –Text based –Graphical user interface (GUI)  window manager Kernel: Internal part of OS which performs basic required functions –File manager –Device drivers –Memory manager –Scheduler and dispatcher

14. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-14 Kernel : File Manager Coordinates the use of the machine’s mass storage facilities Maintains records of all files, including their locations access rights of different users. Directory (or Folder): A user-created bundle of files and other directories (subdirectories) Directory Path: A sequence of directories within directories (eg. animals/prehistoric/dinosaurs)

15. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-15 Kernel : Device Driver Communicates with the controllers/perpheral devices to carry out operations in peripheral devices. Each device driver is designed uniquely for its particular type of device

16. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-16 Kernel : Memory Manager Allocates space in main memory The duty of memory manager is extensive in multitasking or multi user environments What happens if main memory space required exceeds the space actually available computer ? Virtual memory : Storage space on your computer's hard disk that OS uses in conjunction with main memory.

17. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-17 Kernel : Scheduler and Dispatcher Scheduler : In multiprogramming systems (multiple users), it determines which activities are to be considered for execution Dispatcher: Controls the allocation of time to activities in multiprogramming systems

18. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-18 Getting it Started (Bootstrapping) ROM (Read Only Memory): A small portion of main memory which has non-volatile memory cells Firmware: A program stored in ROM Bootstrap: Program in ROM (example of firmware) –Run by the CPU when power is turned on –Directs CPU to transfer OS from mass storage to main memory –Directs CPU to execute jump to OS

19. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-19 Getting it Started (Bootstrapping) Why computers systems are not provided with enough ROM to hold the entire OS?? ANSWER: Not efficient with today’s technology Turnkey systems: Systems which are ready to function with the flip of a switch or turn of a key.

20. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-20 Figure 3.5 The booting process BIOS (Basic-Input-Output-System): A collection of software routines stored in ROM for performing fundamental input/output operations which are used by bootstrap to perform I/O activities before OS becomes functional

21. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-21 Processes Process: The activity of executing a program Process State: Current status of the activity Process state contains –The value of program counter –The values in general purpose registers –The values of related portion of main memory

22. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-22 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.

23. Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 3-23 Figure 3.6 Time-sharing between process A and process B Process switch(context switch): Changing from one process to another Interrupt: Signal generated by dispatcher to indicate the end of the slice Interrupt handler: A part of dispatcher which describes how the dispatcher should respond to the interrupt signal