31 Jan 2014

Os theory set 1

These are basic level questions asked in various companies. This is theory paper for Operating System professionals. You are most welcome to give feedback for these questions in comments sections. 

1.      Explain Belady's Anomaly. TCS
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.

2.      What is the resident set and working set of a process? WIPRO
Resident set is that portion of the process image that is actually in real-memory at a particular instant. Working set is that subset of resident set that is actually needed for execution. (Relate this to the variable-window size method for swapping techniques.)

3.      When is a system in safe state? TCS
The set of dispatchable processes is in a safe state if there exists at least one temporal order in which all processes can be run to completion without resulting in a deadlock.

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