CSE 330
Operating
Systems
SAMPLE Mid Term Exam
Open book, open notes.
1]
There
are two identical processes being run on a system. Each process does the
following:
Executes a CPU burst of 1 sec.
Outputs 1 KByte of data
Executes a CPU burst of 1 sec.
Outputs 1 KByte of data
Executes a CPU burst of 1 sec.
Outputs 1 KByte of data
Executes a CPU burst of 1 sec.
Outputs 1 KByte of data
Executes a CPU burst of 1 sec and terminates.
A] If the output device has a
data rate of 1KByte/sec, find the turnaround time of each process under:
i] FIFO
scheduling (non-preemptive)
ii] Round Robin scheduling (assume the time quanta is small, and the exact
value is
not important.)
B] Now we add a output buffer of 10KBytes to the above system. Find the
turnaround time of each process under:
i] FIFO
scheduling (non-preemptive)
ii] Round Robin scheduling (assume the time quanta is small, and the exact
value is
not important.)
2]
It
is stated that the “Shortest Job First Policy” is optimal.
- What does optimal mean
in this context?
- What property of the
SJF policy is optimal and what property makes it not so desirable?
- Why do not use SJF?
- Prove that the SJF is
optimal with respect to the property in [B]
3]
The
following code fragment is a 2-process “solution” to the critical section
problem.
try[i] =
true;
while (incs[j])
no-op;
while (turn=j and try[j]) no-op;
incs[i] =
true;
critical
section
try[i] =
false;
incs[i] =
false;
turn = j;
[2
- continued]
Does
the above “solution” meet all 3 conditions of critical sections? Please explain
your answer.
4]
There are 4 processes,
executing concurrently. Process P0 is in an infinite loop, incrementing the
value of the variable x (x is initialized to 0). P0 is the only
process that changes the value of x.
The rest of the processes Pi (1 <= i<=3) monitor the value of x. Whenever x reaches a value such that it is divisible by i, Pi prints the value of x.
For example, P3 will print the sequence 3 6 9 12 ….. as
the value of x reaches 3, 6, 9, 12
and so on.
A] Write the code for all the 4
processes using semaphores. Note that P1 - P3 should be identical.
B] Write the code for all the 4
processes using CCRs. Note that P1 - P3 should be identical.