Advanced Operating Systems

1. Advanced Operating Systems • Welcome to this course, in Fall Semester 1389-90 • Main TextBooks 1- Tanenbaum’s book 2- Chow’s Book 3- Singhal’s Book • Other extra references: 1- Attieh’s book 2- Lynch’s book OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

2. Advanced Operating Systems • Assistants: to be announced. • Evaluation: • Mid-Term Exam • Project • Review Paper • Final Exam • The course Home page and Mailing-list … • Office Hours: Sunday and Tuesday 8 - 9 OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

3. 1Introduction to Distributed Systems and Distributed Operating Systems (DOSs)(From Tanenbaum’sBook) OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

4. Definition of a Distributed System (1) A distributed system is: A collection of independent computers that appears to its users as a single coherent system. OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

5. Definition of a Distributed System (2) 1.1 A distributed system organized as middleware.Note that the middleware layer extends over multiple machines.

6. Goals in DSs • Connecting Users and Resources • Transparency • Openness • Scalability Will be discussed in the next slides. OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

7. Transparency in Distributed Systems Different forms of transparency in a distributed system.

8. Degree of Transparency • Is transparency good anytime and everywhere? • Tradeoff between transparency and performance. - Updating a replicated database! OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

9. Openness • Offering services based on standards. • Services are specified through interfaces, described in IDL (Interface Definition Language) • Interoperability: two implementations of a system to co-exist and work together; or multiple systems developed by different vendors to be able to work with each other. • Portability: An application developed to work on A can be executed on another system B. • Separating policy from mechanism OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

10. Scalability • Definition of an scalable system? • 3 different dimensions • Size: Adding more users and resources to the system. • Geography: Users and resources can lie far apart. • Administration: Many administration organization! OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

11. Scalability Obstacles Examples of scalability limitations.

12. Scalability Solutions • Hiding communication latencies: try to avoid waiting for responses to remote service requests  Use Asynchronous Communication • Many applications cannot run on an asynch communication system • Next slide example. • Distribution: DNS as example • Replication: Caching and consistency! OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

13. Scaling Techniques (1) 1.4 • The difference between letting: • a server or • a client check forms as they are being filled

14. Scaling Techniques (2) 1.5 An example of dividing the DNS name space into zones.

15. Hardware Concepts 1.6 Different basic organizations and memories in distributed computer systems

16. Multiprocessors A bus-based multiprocessor. 1.7 • Memory is Coherent. • The bus is overloaded. • Caching: hit-rate? • Scalability? OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

17. Software Concepts An overview of • DOS (Distributed Operating Systems) • NOS (Network Operating Systems) • Middleware OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

18. Uniprocessor Operating Systems Separating applications from operating system code through a microkernel. 1.11 OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

19. Multiprocessor Operating Systems (1) A monitor to protect an integer against concurrent access. monitor Counter { private: int count = 0; public: int value() { return count;} void incr () { count = count + 1;} void decr() { count = count – 1;} } OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

20. Multiprocessor Operating Systems (2) A monitor to protect an integer against concurrent access, but blocking a process. monitor Counter { private: int count = 0; int blocked_procs = 0; condition unblocked; public: int value () { return count;} void incr () { if (blocked_procs == 0) count = count + 1; else signal (unblocked); } void decr() { if (count ==0) { blocked_procs = blocked_procs + 1; wait (unblocked); blocked_procs = blocked_procs – 1; } else count = count – 1; } } OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

21. Multicomputer Operating Systems (1) General structure of a multicomputer operating system Message Passing 1.14 OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

22. Distributed Shared Memory Systems (1) • Pages of address space distributed among four machines • Situation after CPU 1 references page 10 • Situation if page 10 is read only and replication is used OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

23. DSM – An Interesting Scenario! False sharing of a page between two independent processes. 1.18 False Sharing! OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

24. Network Operating System (1) General structure of a network operating system. 1-19 OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

25. Network Operating System (2) Two clients and a server in a network operating system. 1-20 OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

26. Network Operating System (3) Different clients may mount the servers in different places. 1.21 OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

27. Positioning Middleware General structure of a distributed system as middleware. 1-22 OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

28. Middleware and Openness In an open middleware-based distributed system, the protocols used by each middleware layer should be the same, as well as the interfaces they offer to applications. 1.23 OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

29. Comparison between Systems OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

30. Clients and Servers General interaction between a client and a server. 1.25 OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

31. An Example Client and Server (1) The header.h file used by the client and server. OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

32. An Example Client and Server (2) A sample server. OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

33. An Example Client and Server (3) A client using the server to copy a file. 1-27 b OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

34. Application Layering:Processing Level The general organization of an Internet search engine into three different layers 1-28 OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

35. Multitiered Architectures (1) Alternative client-server organizations (a) – (e). 1-29 OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

36. Multitiered Architectures (2) An example of a server acting as a client. 1-30 OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

37. Modern Architectures An example of horizontal distribution of a Web service. 1-31 OS2-Sharif University of Technology - Sem1-89-90; R. Jalili