$1.$ An alternative definition for a distributed system is that of a collection of independent computers providing the view of being a single system, that is$,$ it is completely hidden from users that there even multiple computers. Give an example where this view would come in very handy.

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$2.$ What is the role of middleware in a distributed system?

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$3.$ Explain what is meant by transparency in a distributed system $,$ and give examples of different types of transparency.

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$4.$ Describe precisely what is meant by a scalable system.

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$5.$ Executing nested transactions requires some form of coordination. Explain what a coordinator should actually do$.$

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$6.$ When a transaction is aborted, we have said that the world is restored to its previous state, as though the transaction had never happened. Give an example where resetting the world is impossible.

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$7.$ What is a three$-$tiered client$-$server architecture?

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$8.$ What is the difference between a vertical distribution and a horizontal distribution?

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$9.$ Consider a chain of processes P$1,$ P$2,...,$ Pn implementing a multitiered client$-$server architecture. Process Pi is client of process Pi$+1,$ and Pi will return a reply to Pi$-1$ only after receiving a reply from Pi$+1.$ What are the main problems with this organization when taking a look at the request$-$reply performance at process P$1?$

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$10.$ Not every node in a peer$-$to$-$peer network should become superpeer. What are reasonable requirements that a superpeer should meet?

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$11.$ Would it make sense to limit the number of threads in a server process? Why?

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$12.$ Sketch the design of a multithreaded server that supports multiple protocols using sockets as its transport$-$level interface to the underlying operating system.

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$13.$Suppose that you could make use of only transient synchronous communication primitives. How would you implement primitives for transient asynchronous communication?

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$14.$ Suppose that you could make use of only transient asynchronous communication primitives. How would you implement primitives for transient synchronous communication?

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$15.$ What data structure is needed by the receiver in persistent communications?

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$16.$ In this problem you are to compare reading a file using a single$-$threaded file server and a multithreaded server. It takes $20$ msec to get a request for work, dispatch it$,$ and do the rest of the necessary processing, assuming that the data needed are in a cache in main memory. If a disk operation is needed, as is the case one$-$third of the time, an additional $80$ msec is required, during which time the thread sleeps. How many requests$/$sec can the server handle if it is single threaded? If it is multithreaded?

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$17.$ What are the advantages of using threads over using processes for parallelism?

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$18.$ Briefly discuss the advantages and disadvantages of managing threads in USER mode VS$.$ KERNEL mode

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$19.$ Consider a Hypercube network with $16$ nodes numbered $0$ to $15.$ Show the path a message from node $9$ to $$node $7.$Recall that in a Hypercube there is a link from node I to node J iff their binary representations differ in one bit value.