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 - Sem1-90-91; 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. 1 Introduction to Distributed Systems and Distributed Operating Systems (DOSs) (From Tanenbaum’s Book) 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. OS2-Sharif University of Technology - Sem1-90-91; R. Jalili Definition of a Distributed System (2) A distributed system organized as middleware. Note that the middleware layer extends over multiple machines. 1.1

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. OS2-Sharif University of Technology - Sem1-90-91; R. Jalili Transparency in Distributed Systems Different forms of transparency in a distributed system. TransparencyDescription Access Hide differences in data representation and how a resource is accessed LocationHide where a resource is located MigrationHide that a resource may move to another location Relocation Hide that a resource may be moved to another location while in use Replication Hide that a resource may be shared by several competitive users Concurrency Hide that a resource may be shared by several competitive users FailureHide the failure and recovery of a resource Persistence Hide whether a (software) resource is in memory or on disk

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. OS2-Sharif University of Technology - Sem1-90-91; R. Jalili Scalability Obstacles Examples of scalability limitations. ConceptExample Centralized servicesA single server for all users Centralized dataA single on-line telephone book Centralized algorithmsDoing routing based on complete information

12. Scalability Solutions 1.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. 2.Distribution: DNS as example 3.Replication: Caching and consistency! OS2-Sharif University of Technology - Sem1-89-90; R. Jalili

13. OS2-Sharif University of Technology - Sem1-90-91; R. Jalili Scaling Techniques (1) 1.4 The difference between letting: a)a server or b)a client check forms as they are being filled

14. OS2-Sharif University of Technology - Sem1-90-91; R. Jalili Scaling Techniques (2) 1.5 An example of dividing the DNS name space into zones.

15. OS2-Sharif University of Technology - Sem1-90-91; R. Jalili 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 SystemDescriptionMain Goal DOS Tightly-coupled operating system for multi- processors and homogeneous multicomputers Hide and manage hardware resources NOS Loosely-coupled operating system for heterogeneous multicomputers (LAN and WAN) Offer local services to remote clients Middleware Additional layer atop of NOS implementing general-purpose services Provide distribution transparency 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 - Sem1-90-91; R. Jalili

22. Distributed Shared Memory Systems (1) a)Pages of address space distributed among four machines b)Situation after CPU 1 references page 10 c)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 Item Distributed OS Network OS Middleware- based OS Multiproc.Multicomp. Degree of transparencyVery HighHighLowHigh Same OS on all nodesYes No Number of copies of OS1NNN Basis for communication Shared memory MessagesFilesModel specific Resource management Global, central Global, distributed Per node ScalabilityNoModeratelyYesVaries OpennessClosed Open 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