Книга: Distributed operating systems

PROBLEMS

PROBLEMS

1. The price/performance ratio of computers has improved by something like 11 orders of magnitude since the first commercial mainframes came out in the early 1950s. The text shows what a similar gain would have meant in the automobile industry. Give another example of what such a large gain means.

2. Name two advantages and two disadvantages of distributed systems over centralized ones.

3. What is the difference between a multiprocessor and a multicomputer?

4. The terms loosely-coupled system and tightly-coupled system are often used to described distributed computer systems. What is the different between them?

5. What is the different between an MIMD computer and an SIMD computer?

6. A bus-based multiprocessor uses snoopy caches to achieve a coherent memory. Will semaphores work on this machine?

7. Crossbar switches allow a large number of memory requests to be processed at once, giving excellent performance. Why are they rarely used in practice?

8. A multicomputer with 256 CPUs is organized as a 16?16 grid. What is the worst-case delay (in hops) that a message might have to take?

9. Now consider a 256-CPU hypercube. What is the worst-case delay here, again in hops?

10. A multiprocessor has 4096 50-MIPS CPUs connected to memory by an omega network. How fast do the switches have to be to allow a request to go to memory and back in one instruction time?

11. What is meant by a single-system image?

12. What is the main difference between a distributed operating system and a network operating system?

13. What are the primary tasks of a microkernel?

14. Name two advantages of a microkernel over a monolithic kernel.

15. Concurrency transparency is a desirable goal for distributed systems. Do centralized systems have this property automatically?

16. Explain in your own words the concept of parallelism transparency.

17. An experimental file server is up 3/4 of the time and down 1/4 of the time, due to bugs. How many times does this file server have to be replicated to give an availability of at least 99 percent?

18.  Suppose that you have a large source program consisting of m files to compile. The compilation is to take place on a system with n processors, where n >> m. The best you can hope for is an m–fold speedup over a single processor. What factors might cause the speedup to be less than this maximum?

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