Operating System, Class 4E, 4D, 4F, Final Test

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1. Conditions for Deadlock
There are four conditions that are necessary for deadlock to occur: mutual exclusion, hold and wait, no preemption, and circular wait. With deadlock prevention, the system ensures that deadlock does not occur by preventing one of these conditions from holding. Match each of the following techniques with the one deadlock condition that it prevents.
a. Mutual exclusion
b. Hold and wait
c. No preemption
d. Circular wait
2. Can running each of the following code segments lead to deadlock of process 0 and process 1?
Code Sample 1

Proses 0	Proses 1
lock1.acquire( );	lock1.acquire( );
lock2.acquire( );	lock2.acquire( );
lock1.release( );	lock1.release( );
lock2.release( );	lock2.release( );

Code Sample 2

Proses 0	Proses 1
lock1.acquire( );	lock2.acquire( );
lock2.acquire( );	lock1.acquire( );
lock1.release( );	lock1.release( );
lock2.release( );	lock2.release( );

Code Sample 3

Proses 0	Proses 1
lock1.acquire( );	lock2.acquire( );
lock2.acquire( );	lock2.release( );
lock1.release( );	lock1.acquire( );
lock2.release( );	lock1.release( );

3. Consider the following resource graph. Which processes (A, B, C) and which resources (R, S, T) are deadlocked? What needs to be done to break the deadlock? Briefly explain how you knew that.

4. Name two differences between logical and physical addresses.
5. Consider a system in which a program can be separated into two parts: code and data. The CPU knows whether it wants an instruction (instruction fetch) or data (data fetch or store). Therefore, two base–limit register pairs are provided: one for instructions and one for data. The instruction base–limit register pair is automatically read-only, so programs can be shared among different users. What are the advantages and disadvantages of this scheme?
6. What is the effect of allowing two entries in a page table to point to the same page frame in memory? Explain how this effect could be used to decrease the amount of time needed to copy a large amount of memory from one place to another. What effect would updating some byte on the one page have on the other page?
7. Some systems automatically delete all user files when a user logs off or a job terminates, unless the user explicitly requests that they be kept; other systems keep all files unless the user explicitly deletes them. What are the relative merits of each approach?
8. In some systems, a subdirectory can be read and written by an authorized user, just as ordinary files can be.
a. Describe the protection problems that could arise.
b. Suggest a scheme for dealing with each of the protection problems you named in part a.
9. What problems could occur if a system allowed a file system to be mounted simultaneously at more than one location?
10. How do caches help improve performance? Why do systems not use more or larger caches if they are so useful?
11. Suppose that we agree that 1 kilobyte is 1,024 bytes, 1 megabyte is 1,0242 bytes, and 1 gigabyte is 1,0243 bytes. This progression continues through terabytes, petabytes, and exabytes (1,0246). There are currently several new proposed scientific projects that plan to record and store a few exabytes of data during the next decade. To answer the following questions, you will need to make a few reasonable assumptions; state the assumptions that you make.
1 FDD = 1.44MB, 1 CD = 700MB, 1 HDD=120GB
a. How many FDD would be required to hold 4 exabytes of data?
b. How many CD would be required to hold 4 exabytes of data?
d. How many hdd storages would be required to hold 4 exabytes of data ?
12. What is DMA ? How does DMA increase system concurrency? How does it complicate hardware design?
13. Process migration within a heterogeneous network is usually impossible, given the differences in architectures and operating systems. Describe a method for process migration across different architectures running:
a. The same operating system
b. Different operating systems
14. What do you know about OS such as Linux, Windows, and Mac OS? What are the differences of them? List any other OS you know.
15. If you asked to build an operating system, explain the OS you willing to build.