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Operating Systems Multiple Choice Questions - Set 7
1. Which of the following is a disadvantage
of user level threads?
(a) User-level thread does
not require modification to operating systems.
(b) Thread switching is
not expensive than a procedure call.
(c) User-level threads can
be implemented on a OS that does not support threads.
(d) User level threads require non blocking system calls
Answer: (d)
User-level
threads require non-blocking systems call i.e., a multithreaded kernel.
Otherwise, entire process will blocked in the kernel, even if there are runnable
threads left in the processes. For example, if one thread causes a page
fault, the process blocks.
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2. What is normally meant by a “context
switch”?
(a) Any change in state of
a process as it executes.
(b) Saving the state of one process and restoring the state of
another process so that the CPU moves from running one process to running the
other.
(c) The switch between a
process running in user mode to running in kernel mode. This can happen as the
result of a system call or an exception.
(d) The change which
occurs on the stack of a running process as it makes a function call, including
the allocation of memory for any parameters and the local variables.
Answer: (b)
The change from
one process running to another one running on the same processor is usually
referred to as a "context switch".
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3. Given three processes A, B, and C with
corresponding burst times 20, 5, and 2, what is the average waiting time with a
first come first served (FCFS) scheduler? All processes are ready to run at the
same time but they arrived in the order A, B, then C.
(a) 3
(b) 15
(c) 9
(d) 25
Answer: (b)
The Gantt chart
for the given schedule is;
0 20 25 27
Average waiting
time = (0+20+25)/3 = 15.
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4. Which of the following is NOT an
advantage of system-level threads over user-level threads?
(a) Threads from the same
process can run simultaneously on different cores/processors
(b) Each thread can be
scheduled separately
(c) Switching between threads is faster
(d) Blocking threads don’t
stop the entire process
Answer: (c)
User-level
threads are easier and faster to create than kernel-level threads. They can
also be more easily managed.
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5. The definition “an instance of a program in execution” best
applies to which of the following?
(a) a thread
(b) a process
(c) a system-level
resource
(d) a user-level resource
Answer: (b)
A process is an
instance of a program in execution. An active program can be called a
Process. Process contains the program code and its activity.
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