Operating systems exams - multiple choice questions (MCQ) and answers
Operating
Systems MCQ questions and answers – Set 15
1. Which of the following instructions should be privileged?
(a)
Disable interrupts
(b) Read the real-time
clock
(c)
Switch from user mode to kernel mode
(d) Switch from kernel
mode to user mode
View Answer
Answer: (a) Disable
interrupts and (c) Switch from user to kernel mode
Disable interrupts should be privileged, otherwise a process could grab and hold the processor.Switch from user mode to kernel mode, otherwise a process can enter kernel mode at any time. |
2. Which of the following should be found in a Process Control Block (PCB)?
(a) Process state
(b) Accounting information
(c) Open files
(d)
All of the above
View Answer
Answer: (d) All of the
above
Process Control Block (PCB)
A
process control block (PCB) is a data structure used by computer operating
systems to store all the information about a process. It is also known as a
process descriptor.
PCB
contains various information regarding a process;
|
3. Which of the following is a property
of a hard real-time system?
(a) Critical real-time
tasks get priority over other tasks and retain that priority until execution
time has been completed.
(b) Lack deadline support
(c) Easily support
advanced operating system features
(d)
Guarantees that critical tasks are completed on time
View Answer
Answer: (d) Guarantees
that critical tasks are completed on time
.
|
4. What is the average waiting time using
the SJF scheduling algorithm given that process P1 through P3 have burst times
of 20ms, 10ms, and 35ms respectively?
(a) 10 ms
(b)
13.3 ms
(c) 21.6 ms
(d) 35 ms
View Answer
Answer: (b) 13.3 ms
The shortest job is P2 with 10 ms
burst time, the next shortest is P1 with 20 ms and the next one is P3 with 35
ms. The processor with shortest burst time will gets turn first.
The Gantt chart for the given
schedule is;
Average waiting time = (0+10+30)/3 =
40/3 = 13.3.
|
5. What is the average waiting time using
the FCFS scheduling algorithm given that process P1 through P3 have burst times
of 12ms, 3ms, and 6ms respectively?
(a) 7 ms
(b) 4 ms
(c)
9 ms
(d)
8 ms
View Answer
Answer: (c) 9 ms
The Gantt chart for the given
schedule is;
Average waiting time = (0+12+15)/3 =
9.
|
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