Operating Systems

1. Operating Systems

2. Definition • An operating system is a collection of programs that manage the resources of the system, and provides a interface between the user, the hardware, and the applications.

3. Types of Operating Systems • Simple • device control • embedded on a ROM chip • Complex • Windows • NT • Unix, Etc.

4. Complex Operating Systems • Consist of multiple programs • The Kernel is the core of the operating systems.

5. Kernel • The kernel is responsible for: • Device control • Memory management • Scheduling • Inter-process communication • Processing of interrupts and exceptions.

6. Single vs. Multiple Processor • Single Processor can only run one instruction at a time. • It gives the appearance of multi-tasking with switching.

7. 2 Types of Switching • Co-Operative Switching • Pre-Emptive Switching

8. Co-Operative Switching • In co-operative switching the task which is currently running must voluntarily give up the processor for the next process to run.

9. Problem with Co-Operative Switching • If first process “hangs up” and does not give up control the computer freezes. No other task can run.

10. Pre-Emptive Switching • In pre-emptive switching the task that is currently running is forced to give up control after a certain period of time. If a task “hangs” it does not stop subsequent task from running.

11. Pre-Emptive Switching is“Better” than Co-Operative Switching

12. 16-Bit vs. 32-bit • 32-bit programs use pre-emptive switching. • 16-bit program use co-operative switching and are more susceptible to “freezing”.

13. Context Switching • The process of switching from one task to another is called “Context Switching”.

14. Scheduling • Scheduling is the process of deciding which task should run next.

15. Time Slice • The amount of time that a process runs before giving up control is called time slice or quantum period.

16. Co-Operative Processing • In co-operative processing the processes are generally arranged such that as the top process is completed each task moves up one place.

17. Pre-Emptive Scheduling • Pre-emptive scheduling uses a real-time clock, which generates interrupts at regular intervals. Each time an interrupt occurs the processor is switched to another task. • Generally tasked are assigned a priority in pre-emptive scheduling.

18. Multiprocessor vs. Multiprocessing • A multi-processor computer is a computer with more than one processor.

19. Categories of Multi-Processor Computers • Shared memory multi-processor • Distributed memory multi-processor

20. Shared Memory Multi-processor • Shared memory multi-processors have multiply CPUs, and they all share the same memory. • Communication between the processors is easy to implement, but care must be taken to synchronize memory access.

21. Distributed Memory Multi-Processors • Also has multiple CPUs, but each CPU has its own memory. • In distributed memory multi-processor memory synchronization is not a problem, • but communication between the processors is often slow and complicated.

22. Related to Multi-Processors • Networked Systems • Distributed Systems

23. Networked Systems • Networked systems consist of multiple computers, networked together. Users are aware of the different computers that make up the system.

24. Distributed Systems • Distributed systems also consist of multiple computer but unlike the networked system the various computers are transparent to the user.

25. Operating System • A computer is a set of resources for the movement, storage, and processing of data. • The operating system is responsible for • managing these resources • scheduling the other programs • and providing the user interface.