Sample midterm exam
In a multi-process system, at any moment every process is in
one of three states: running, ready, or blocked. What are the transitions
between these states, and when do they occur?
Explain briefly (1 or 2 sentences) the major difference
between a thread and a process. Name one type of state that is recorded
in a thread table. Name one type of information that is saved in
a process table but not in a thread table.
Problem 3 (Multiple choice: Give all correct answers)
Suppose there are two processes, A and B, which share semaphors
R and S. At the starting time, R = 0, S = 1. A and B are entering the
sections of code shown below:
Process A: Process B:
P(R); Operation B.1;
Operation A.1; Operation B.2;
Operation A.2; Operation B.3;
Which of the following statements are true (more than one may be true:)
- A. Operation A.1 cannot start until operation B.1 is complete.
- B. Operations A.1 and B.2 cannot execute simultaneously.
- C. Operations A.1 and B.3 cannot execute simultaneously
- D. Operations A.2 and B.3 cannot execute simultaneously
- E. The system may deadlock.
Problem 4: What is spooling, and why is it used?
Problem 5 (Multiple choice: 1 correct answer.)
A ``critical section'' of code is
- A. A section that is executed very often, and therefore should
be written to run very
- B. A section of the program that must not be interrupted by the
- C. A section of the program that is susceptible to race conditions,
unless mutual exclusion is enforced.
- D. A section of the code executed in kernel mode.
Problem 6: (Multiple choice: Give all correct answers)
A given OS uses round-robin scheduling. The time quantum
is Q and the time needed for context switch is C. Over an extended
time period T, which is much greater than Q+C, there are
N active processes; no processes begin or terminate during this period.
Assume further that all these processes fit together in memory; no
swapping or paging is needed.
Which of the following statements are true:
A. All processes get an equal share of the CPU.
B. If process P is ready, then it will be scheduled to run within time
NC + (N-1)Q.
C. If process P has just exhausted its time quota, then it will have to
wait for at least
time NC + (N-1)Q.
D. If process P is running and blocks, and process W is currently ready
then W will be
run before P runs again.
E. The efficiency of the system --- that is, the fraction of time that the
CPU is executing
a process --- is always equal to Q/(Q+C).
Suppose that jobs arrive according to the following schedule.
Process Starting Time Run Time
A 0 12
B 3 7
C 6 2
D 8 5
E 9 2
F 12 12
Trace the progress of the system if the scheduler used is
- First come first served.
- Shortest job next
- Shortest remaining time next