Operating Systems

1. Operating Systems Dr. Raihan Ur Rasool BICSE-3 Credits: 3

2. Contacts • Office: • Academic Block -II Phone 051-9280439 Ext 129 • Office Hours: • Monday 1000 – 1200 hrs • email: • dr.raihan@niit.edu.pk • Exceptional meeting: • Give me an email and get time. Operating System Concepts

3. Course Outline • Introduction • Operating System Structures • Processes • Threads • CPU Scheduling • Process Synchronization • Deadlocks • Main Memory • Virtual Memory • File-System Interface • File-System Implementation • Mass-Storage Structure • I/O Systems Operating System Concepts

4. Books • Text Books • Operating System Concepts, 7th Edition, by Avi Silberschatz, Peter Baer Galvin, Greg Gagne, published by John Wiley & Sons, Inc. ISBN 0-471-69466-5 Operating System Concepts

5. Books • Reference Books • Operating Systems by Williams Stallings • www.howstuffworks.com • www.whatis.com Operating System Concepts

6. Evaluation One Hour Tests (OHT) : 30% Assignments : 10% Quizzes : 5% Project : 10% End Semester Examination (ESE) : 45% Operating System Concepts

7. Policies • Bring your own calculator, pen paper etc.. • You will not be allowed to borrow anything from anyone during any test • Must write your name and reference number (Merit No or Regn No) in a test • No late work will be accepted (unless arrangements have been made in advance) • Ask questions; participate actively in class • You are allowed to talk to instructor only Operating System Concepts

8. Policies • You are responsible for what is covered in class – even if you don’t show up • Deficiency in attendance may lead to termination or relegation • You are encouraged to help each other with your homework assignments – but you must turn in your own work • If you are found to be cheating, you will fail at least the assignment / test and perhaps the entire class Operating System Concepts

9. Policies • If you have any learning disabilities or special needs, please let me know in advance through email or personal meeting • Check your email regularly for messages • Quizzes are unannounced Operating System Concepts

10. Chapter 1: Introduction • What is an Operating System? • Mainframe Systems • Desktop Systems • Multiprocessor Systems • Distributed Systems • Clustered System • Real -Time Systems • Handheld Systems • Computing Environments Operating System Concepts

11. What is an Operating System? • A program that acts as an intermediary between a user of a computer and the computer hardware. • Operating system goals: • Execute user programs and make solving user problems easier. • Make the computer system convenient to use. • Use the computer hardware in an efficient manner. • E.g. • Microsoft Windows 98/2000/XP • Linux (Different flavors, RedHat most popular) • Unix (FreeBSD Popular) • Solaris (Based on Unix, expensive but very reliable) • MacOS (Apple , Motorola 68K series) • Micro C Linux (Flavor of linux for Hand held devices) Operating System Concepts

12. Computer System Components 1. Hardware – provides basic computing resources (CPU, memory, I/O devices). 2. Operating system – controls and coordinates the use of the hardware among the various application programs for the various users. 3. Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs). 4. Users (people, machines, other computers). Operating System Concepts

13. Operating System Definitions • Resource allocator – manages and allocates resources. • Processor (CPU) • Memory • Disk Space • Modem, Network etc. • Control program – controls the execution of user programs and operations of I/O devices . • C/C++ Programs • MS Office etc. • Kernel – A program running at all the times (all else being application programs). • Always resident in RAM (Like soul of human) • E.g. Command.com in MS-DOS • In Windows system kernel is not just one program but it is a set of programs (We will look at Windows XP and Linux in a little more detail in future lectures) Operating System Concepts

14. Abstract View of System Components OS – an environment provider Operating System Concepts

15. Different Computer Systems • Mainframe Systems • Batch Systems • Multiprogrammed Systems • Time-Sharing Systems • Desktop Systems • Multiprocessor Systems • Distributed Systems Operating System Concepts

16. Mainframe Systems • First computers used to tackle commercial and engineering applications. • 0th Generation (1940’s) • Very large computers (Size of a big room) • Required a team to run / manage the whole system Operating System Concepts

17. Batch Systems Mainframe Systems • Reduced setup time by batching similar jobs • Batches were sorted and fed into the system by Operator. • E.g. Updating daily sales records in a database etc. • Processed one program at a time and after finishing the program loaded another program from the same batch. • Automatic job sequencing – automatically transfers control from one job to another. First basic operating system. Operating System Concepts

18. Memory Layout for a Simple Batch System Operating System Concepts

19. Batch Systems Card Reader Card Reader Card Reader Printer CPU Operating System Concepts

20. Multiprogrammed Batch Systems • Multiprogramming increases CPU utilization by organizing jobs so that the CPU always has one to execute – Early 1960 • Job scheduling and CPU scheduling • If Job 1 is being executed and then due to some reason it has to wait for some I/O Operation, then the CPU would automatically switch to Job 2 and would turn to Job 3 or Job 1 according to algorithm if job 2 has to perform I/O. • Usually a process (program in the memory of CPU) has to perform I/O after a few calculations DISK Job1, Job 2, Job 3 … Job n Operating System Concepts

21. Multiprogrammed Systems Mainframe Operating System (OS) DISK Job 1, Job 2, . . . Job n Job 1 Job 1 Job 2 Job 2 Job 3 Job 3 Operating System Concepts

22. OS Features Needed for Multiprogramming • I/O routine supplied by the system. • Memory management – the system must allocate the memory to several jobs. • CPU scheduling – the system must choose among several jobs ready to run. • Allocation of devices. Operating System Concepts

23. Time-Sharing Systems–Interactive Computing • The CPU is multiplexed among several jobs that are kept in memory and on disk (the CPU is allocated to a job only if the job is in memory). • A job swapped in and out of memory to the disk. • On-line communication between the user and the system is provided; when the operating system finishes the execution of one command, it seeks the next “control statement” from the user’s keyboard. • On-line system must be available for users to access data and code. Operating System Concepts

24. Desktop Systems • Personal computers – computer system dedicated to a single user (1970’s). • I/O devices – keyboards, mice, display screens, small printers. • User convenience and responsiveness. • Can adopt technology developed for larger operating system’ often individuals have sole use of computer and do not need advanced CPU utilization of protection features. • May run several different types of operating systems (Windows, MacOS, UNIX, Linux, Solaris, BeOS) • 90% share is for Microsoft Windows based OS • Linux is gaining popularity (Open source) Operating System Concepts

25. Parallel Systems • Multiprocessor systems with more than one CPU in close communication. • Tightly coupled system – processors share memory and a clock; communication usually takes place through the shared memory. • Advantages of parallel system: • Increased throughput • Economical • Increased reliability • graceful degradation • fail-soft systems Operating System Concepts

26. Parallel Systems (Cont.) • Symmetric multiprocessing (SMP) • Each processor runs an identical copy of the operating system. • Many processes can run at once without performance deterioration. • Most modern operating systems support SMP • Asymmetric multiprocessing • Each processor is assigned a specific task; master processor schedules and allocates work to slave processors. • More common in extremely large systems Operating System Concepts

27. Symmetric Multiprocessing Architecture Operating System Concepts

28. Distributed Systems • Distribute the computation among several physical processors. • Loosely coupled system – each processor has its own local memory; processors communicate with one another through various communications lines, such as high-speed buses or telephone lines. • Advantages of distributed systems. • Resources Sharing • Computation speed up – load sharing • Reliability • Communications Operating System Concepts

29. Distributed Systems (cont) • Requires networking infrastructure. • Local area networks (LAN) or Wide area networks (WAN) • May be either client-server or peer-to-peer systems. Operating System Concepts

30. General Structure of Client-Server Operating System Concepts

31. Clustered Systems • Definition: Clustered computers which share storage and are closely linked via LAN networking. • Advantages: high availability, performance improvement, etc. • Clustering allows two or more systems to share storage. • Provides high reliability. • Asymmetric clustering: one server runs the application while other servers standby. • Symmetric clustering: all N hosts are running the application. Operating System Concepts

32. Real-Time Systems • Definition: A real-time system is a computer system where a timely response by the computer to external stimuli is vital! • Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems. • Well-defined fixed-time constraints. • Real-Time systems may be either hard or soft real-time. Real-time means on-time instead of fast Operating System Concepts

33. Real-Time Systems (Cont.) • Hard real-time system: The system has failed if a timing constraint, e.g. deadline, is not met. • All delays in the system must be bounded. • Many advanced features are absent. • Secondary storage limited or absent, data stored in short term memory, or read-only memory (ROM) • Conflicts with time-sharing systems, not supported by general-purpose operating systems. • E.g. Robot manufacturing a car, Overhead crane loading and unloading at Sea Port, Computer interfacing of certain machines • Soft real-time system: Missing a timing constraint is serious, but does not necessarily result in a failure unless it is excessive • A critical task has a higher priority. • Supported in most commercial OS. • Useful in applications (multimedia, virtual reality) requiring advanced operating-system features. Operating System Concepts

34. Handheld Systems • Personal Digital Assistants (PDAs) • Cellular telephones • Issues: • Slow processors  Battery Power • Limited memory  No virtual Memory, Small size • Small display screens  Web clipping, Operating System Concepts

35. Migration of Operating-System Concepts and Features Operating System Concepts

36. Computing Environments • Traditional computing • Web-Based Computing • Embedded Computing Operating System Concepts

37. End Of Lecture Next Lecture Computer System Operation I/O Structure Storage Structure Storage Hierarchy Operating System Concepts