Computer Science 425 Distributed Systems CS 425 / CSE 424 / ECE 428 Fall 2010Our Main Goal TodayCan you name some examples of Operating Systems?Slide 4What is an Operating System?Slide 6FOLDOC definitionCan you name some examples of Distributed Systems?Slide 9What is a Distributed System?Slide 11Textbook definitionsUnsatisfactorySlide 14Slide 15Slide 16A working definition for usDistributed System Example – Web servers + clientsDistributed System Example – Gnutella Peer to Peer SystemThe Internet – Quick RefresherAn Intranet underneath a distributed file systemDistributed Systems are layered over networksThe Secret of the World Wide Web: the HTTP ProtocolThe HTTP Protocol: MoreHTTP ExampleHTTP Example (cont.)Trying Out HTTP (Client Side) for YourselfDoes our Working Definition work for the http Web?“Important” Distributed Systems IssuesThere are a range of interesting problems for Distributed System designersTypical Distributed Systems Design Goals“Important” Issues“Concepts”?How will you Learn?On the TextbookWhat assistance is available to you?You can meet us anytimeReadingsLecture 1-1Lecture 1-1Computer Science 425Distributed SystemsCS 425 / CSE 424 / ECE 428Fall 2010Computer Science 425Distributed SystemsCS 425 / CSE 424 / ECE 428Fall 2010Indranil Gupta (Indy)August 24, 2010Lecture 1 2010, I. Gupta, K. Nahrtstedt, S. Mitra, N. Vaidya, M. T. Harandi, J. HouWebsite: http://www.cs.uiuc.edu/class/fa10/cs425/Lecture 1-2Lecture 1-2Our Main Goal TodayOur Main Goal TodayTo Define the Term Distributed SystemLecture 1-3Lecture 1-3Can you name some examples of Operating Systems?Can you name some examples of Operating Systems?Lecture 1-4Lecture 1-4Can you name some examples of Operating Systems?Can you name some examples of Operating Systems?…Linux WinXPVista Unix FreeBSD Snow Leopard2K Aegis Scout Hydra Mach SPINOS/2 Express Flux Hope SpringAntaresOS EOS LOS SQOS LittleOS TINOSPalmOS WinCE TinyOS Android…Lecture 1-5Lecture 1-5What is an Operating System?What is an Operating System?Lecture 1-6Lecture 1-6What is an Operating System?What is an Operating System?•User interface to hardware (device driver)•Provides abstractions (processes, file system)•Resource manager (scheduler)•Means of communication (networking)•…Lecture 1-7Lecture 1-7FOLDOC definitionFOLDOC definition•The low-level software which handles the interface to peripheral hardware, schedules tasks, allocates storage, and presents a default interface to the user when no application program is running.•The OS may be split into a kernel which is always present and various system programs which use facilities provided by the kernel to perform higher-level house-keeping tasks, often acting as servers in a client-server relationship.•Some would include a graphical user interface and window system as part of the OS, others would not. The operating system loader, BIOS, or other firmware required at boot time or when installing the operating system would generally not be considered part of the operating system, though this distinction is unclear in the case of a roamable operating system such as RISC OS.•The facilities an operating system provides and its general design philosophy exert an extremely strong influence on programming style and on the technical cultures that grow up around the machines on which it runs.(FOLDOC = Free On-Line Dictionary of Computing)Lecture 1-8Lecture 1-8Can you name some examples of Distributed Systems?Can you name some examples of Distributed Systems?Lecture 1-9Lecture 1-9Can you name some examples of Distributed Systems?Can you name some examples of Distributed Systems?•Client-Server (NFS)•The Web•The Internet•An ad-hoc network•A sensor network•DNS•Gnutella or BitTorrent (peer to peer overlays)•A datacenter, e.g., The Planet, or Amazon EC2/S3•(The Solar System?)•(Society?)•(Food Chain?)Lecture 1-10Lecture 1-10What is a Distributed System?What is a Distributed System?Lecture 1-11Lecture 1-11FOLDOC definitionFOLDOC definitionA collection of (probably heterogeneous) automata whose distribution is transparent to the user so that the system appears as one local machine. This is in contrast to a network, where the user is aware that there are several machines, and their location, storage replication, load balancing and functionality is not transparent. Distributed systems usually use some kind of client-server organization.Lecture 1-12Lecture 1-12Textbook definitionsTextbook definitions•A distributed system is a collection of independent computers that appear to the users of the system as a single computer [Andrew Tanenbaum] •A distributed system is several computers doing something together. Thus, a distributed system has three primary characteristics: multiple computers, interconnections, and shared state[Michael Schroeder]Lecture 1-13Lecture 1-13UnsatisfactoryUnsatisfactory•Why are these definitions short? •Why do these definitions look inadequate to us?•Because we are interested in the insides of a distributed system–design and implementation–maintenance–study–Algorithmics (“protocols”)Lecture 1-14Lecture 1-14“I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description; and perhaps I could never succeed in intelligibly doing so. But I know it when I see it, and the motion picture involved in this case is not that.”[Potter Stewart, Associate Justice, US Supreme Court (talking about his interpretation of a technical term laid down in the law, case Jacobellis versus Ohio 1964) ]Lecture 1-15Lecture 1-15(A) Plants and Animals interacting in the Food Chain(A)Which is a Distributed System – (A) or (B)?Which is a Distributed System – (A) or (B)?Lecture 1-16Lecture 1-16(B) The Internet (Internet Mapping Project, color coded by ISPs)(B)Lecture 1-17Lecture 1-17A working definition for usA working definition for usA distributed system is a collection of entities, each of which is autonomous, programmable, asynchronous and failure-prone, and which communicate through an unreliable communication medium.•Our interest in distributed systems involves –design and implementation, maintenance, study, algorithmics•Entity=a process on a device (PC, PDA)•Communication Medium=Wired or wireless networkLecture 1-18Lecture 1-18Distributed System Example – Web servers + clientsDistributed System Example – Web servers + clientsSource:
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