May-2010 Question Paper Subject:- OSCD
1. What are the various real-time CPU scheduling algorithms.
Explain each one in brief.
Ans:
Explain
P=
D=
T=
Types of Real Time CPU Scheduling:1. RATE –MONOTONIC Scheduling
2. Earliest Deadline First Scheduling
3. Priority Inversion
May-2010 Question Paper Subject:- OSCD
2. What are requirements of mutual exclusion? Explain
Peterson's algorithm for mutual exclusion.
Ans:
•
No two processes simultaneously in critical region
•
No assumptions made about speeds or numbers of CPUs
•
No process running outside its critical region may block another process
•
No process must wait forever to enter its critical region
void P0() {
while (true) {
flag [0] = true;
turn = 1;
while (flag [1] && turn == 1)
/* do nothing */;
/* critical section */;
flag [0] = false;
/* remainder */;
}
}
May-2010 Question Paper Subject:- OSCD
3. What are two differences between user-level threads and
Kernel-level threads? Under what circumstances is one type
better than the other?
Ans:
Differences between user-level threads and kernel-level threads (Any two):
•
Operating system has the knowledge of existence of kernel level threads while it does not know
about the existence of user-level threads.
•
Suppose a process P1 has 2 kernel level threads and P2 has 2 user-level threads. If one thread
in P1 gets blocked, its second thread is not affected. But in case of P2 if one thread is blocked
(say for I/O), the whole process P2 along with the 2nd thread gets blocked.
•
Kernel level threads are slower to create compared to user-level threads.
•
Switching in Kernel level thread involves OS scheduler while in user-level threads OS scheduler
is not involved.
•
Context switching between kernel level threads has high overhead, almost the same as a
process.
•
Context switching between user-level threads has almost no overhead as compared to kernel
level threads.
•
Kernel level threads can run on different processors simultaneously while user-level threads of
a process will run on one processor only even if multiple processors are available.
May-2010 Question Paper Subject:- OSCD
4. Consider the following page reference string :1,2,3,4,2,1,5,6,2,1,2,3,7,6,3,2,1,2,3,6
How many page faults would occur for the following replacement algorithms
assuming one, two, three, four, five, six or seven frames?
- LRU Replacement
- FIFO Replacement
-Optimal Replacement.
Ans:
May-2010 Question Paper Subject:- OSCD
5. How does DMA increase system concurrency? How does it complicate
hardware design?
Ans:
DMA increases system concurrency by allowing the CPU to perform tasks
while the DMA system transfers data via the system and memory busses.
Hardware design is complicated because the DMA controller must be
integrated into the system, and the system must allow the DMA controller
to be a bus master.
Cycle stealing may also be necessary to allow the CPU and DMA controller to
share use of the memory bus.
May-2010 Question Paper Subject:- OSCD
6. How do caches help improve performance? Why do systems not use
more or larger caches if they are so useful?
May-2010 Question Paper Subject:- OSCD
7. What are the various disk-scheduling algorithms. Explain each one in
brief.
Ans:
FCFS
SSTF
SCAN
C-SCAN
May-2010 Question Paper Subject:- OSCD
Consider the following segment table:
Segment
Base Length
0
219
600
1
2300
14
2
90
100
3
1327
580
4
1952
96
What are the physical addresses for the following logical addresses?
a. 0,430
b. 1,10 c. 2,500
d. 3,400
e. 4,112
Ans:
a.
b.
c.
d.
e.
219 + 430 = 649
2300 + 10 = 2310
illegal reference, trap to operating system
1327 + 400 = 1727
illegal reference, trap to operating system
May-2010 Question Paper Subject:- OSCD
9 What are the four conditions that create deadlock? Explain
deadlock prevention and avoidance techniques
Ans:
Conditions for Deadlock
Mutual exclusion: resources cannot be shared.
Hold and wait: processes request resources incrementally, and hold on to what
they've got.
No preemption: resources cannot be forcibly taken from processes.
Circular wait: circular chain of waiting, in which each process is waiting for a
resource held by the next process in the chain.
Deadlock Prevention
Attacking all the above condition for not occuring
Deadlock Avoidance
Banker Algo (Both Safety and Resource Allocation)
May-2010 Question Paper Subject:- OSCD
10. Given memory partitions of 100K, 500K, 200K, 300K, and 600K (in order), how
would each of the First-fit, Best-fit, and Worst-fit algorithms place processes of
212K, 417K, 112K, and 426K (in order)?
Which algorithm makes the most efficient use of memory?
Ans:
First-fit
Best-fit
Worst-fit
212K is put in 500K
212K is put in 300K
212K is put in 600K
417K is put in 600K
417K is put in 500K
417K is put in 500K
112K is put in 288K
112K is put in 200K
112K is put in 388K
426K must wait
426K is put in 600K
426K must wait
In this example, Best-fit turns out to be the best
May-2010 Question Paper Subject:- OSCD
11. What are the various buffering techniques? Explain each one in detail
May-2010 Question Paper Subject:- OSCD
12. Explain file allocation methods in details
Ans:
Contiguous Allocation
Chained list Allocation
Indexed allocation
May-2010 Question Paper Subject:- OSCD
Write a short notes on any four of the following :(a) Monolithic Vs. Micro Kernels
(b) Comparison of any two RTOS
(c) V Works 5.X
(d) NOS Vs. DOS
(e) Race Condition
(f) Inodes.
Ans:
Race Condition :
Two or more threads read/write a shared variable, and final result
depends on the order of the execution of those threads.
May-2010 Question Paper Subject:- OSCD
1. What are the various real-time CPU scheduling algorithms.
Explain each one in brief.
Ans:
Explain
P=
D=
T=
Types of Real Time CPU Scheduling:1. RATE –MONOTONIC Scheduling
2. Earliest Deadline First Scheduling
3. Priority Inversion