Operating Systems Questions

Q:

What is page cannibalizing?

Answer

Page swapping or page replacements are called page cannibalizing.

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Q:

Explain Belady's Anomaly?

Answer

Also called FIFO anomaly. Usually, on increasing the number of frames allocated to a process virtual memory, the process execution is faster, because fewer page faults occur. Sometimes, the reverse happens, i.e., the execution time increases even when more frames are allocated to the process. This is Belady's Anomaly. This is true for certain page reference patterns.

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Q:

A UNIX user named Bob wants to replace his chess program with a new one, but he is not sure where the old one is installed. Bob is currently able to run a Java chess program starting from his home directory /home/bob using the command: java -classpath /test:/home/bob/downloads/*.jar games.Chess Bob's CLASSPATH is set (at login time) to: /usr/lib:/home/bob/classes:/opt/java/lib:/opt/java/lib/*.jar What is a possible location for the Chess.class file?

 

A) /test/Chess.class B) /home/bob/Chess.class
C) /test/games/Chess.class D) /user/lib/games/Chess.class
 
Answer & Explanation Answer: D) /user/lib/games/Chess.class

Explanation:

/user/lib/games/Chess.class could be the possible location of the file

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Q:

What are the disadvantages of context switching?

Answer

Time taken for switching from one process to other is pure over head. Because the system does no useful work while switching. So one of the solutions is to go for threading when ever possible.

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Q:

What is the cause of thrashing? How does the system detect thrashing? Once it detects thrashing, what can the system do to eliminate this problem?

Answer

Thrashing is caused by under allocation of the minimum number of pages required by a process, forcing it to continuously page fault. The system can detect thrashing by evaluating the level of CPU utilization as compared to the level of multiprogramming. It can be eliminated by reducing the level of multiprogramming.

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