Saturday, April 18, 2020

Multiple choice questions MCQs in Operating System Process management

Multiple choice questions MCQs in OS, Important questions in process management of operating systems course.

Multiple Choice Questions in Operating Systems - Process Management

1. Process A is waiting for the result produced by process B. Also, process A has higher priority than B. So the OS prefers process A and refuses to give CPU time to B. Therefore, both A and B are stuck. What is this scenario called?
(a) Starvation
(b) Deadlock
(c) Livelock
(d) None of the above

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Answer: (a)            
Starvation is a condition where a process does not get the resources it needs for a long time because the resources are being allocated to other processes. It generally occurs in a Priority based scheduling System. Where High Priority requests get processed first. Thus a request with least priority may never be processed.

2. Which of the following components ensures that process can execute within its own address space?
(a) I/O Device
(b) Memory addressing hardware
(c) Stack pointers
(d) All of the above

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Answer: (b)           
Memory addressing hardware ensures that the process can execute within its own address space.

3. Let the time taken to switch between user and kernel modes of execution be t1 while the time taken to switch between two processes be t2. Which of the following is TRUE?
(a) t1 > t2
(b) t1 = t2
(c) t1 < t2
(d) Nothing can be said about the relation between t1 and t2

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Answer: (c)            
Time taken to switch two processes is very large as compared to time taken to switch between kernel and user mode of execution because : Switch between processes or context switch needs saving the PCB of previous process , saving registers and then loading the PCB of new process and its registers etc. However, switch between kernel and user mode of execution, the OS has to just change a single bit at hardware level which is very fast operation.

4. Pipe is used for inter-process communication. Which statements about PIPE are true?
(a) We may read and write from pipe at the same time
(b) pipe is used for unidirectional flow of data
(c) The pipe() system call requires an array of two integers as parameter
(d) All of the above

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Answer: (d)           
pipe in inter-process communication
pipe() is a system call that facilitates inter-process communication. It opens a pipe, which is an area of main memory that is treated as a "virtual file". The pipe can be used by the creating process, as well as all its child processes, for reading and writing.
One process can write to this "virtual file" or pipe and another related process can read from it.
If a process tries to read before something is written to the pipe, the process is suspended until something is written.
The pipe system call finds the first two available positions in the process's open file table and allocates them for the read and write ends of the pipe. Recall that the open system call allocates only one position in the open file table.

5. Consider three CPU-intensive processes, which require 10, 20 and 30 time units and arrive at times 0, 2 and 6, respectively. How many context switches are needed if the operating system implements a shortest remaining time first scheduling algorithm? Do not count the context switches at time zero and at the end.
(a) 1
(b) 2
(c) 3
(d) 4

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Answer: (b)           
Simply a preemptive version of SJF: preempt the running process if a new process arrives with a CPU burst length less than the remaining time of the current executing process.
Process execute in this way.
0 to 10 time units process p1 then switching, 11 to 30 time units process p2 then switching, and 31 to 60 process p3.
Only two context switching possible (since we did not consider the starting and ending switching or even the OS scheduler switching)


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