ALCCS
NOTE:
· Question 1 is compulsory and
carries 28 marks. Answer any FOUR questions from the rest. Marks are indicated against each question.
· Parts of a question should be
answered at the same place.
Q.1 (7
4)
a. Which of the following
instructions are privileged?
(i) Set value of timer.
(ii) Read the clock.
(iii) Clear memory.
(iv) Issue a trap instruction.
(v) Turn
off interrupts.
(vi) Modify entries in device-status table.
(vii) Switch from user to kernel mode.
(viii) Access I/O device.
b. What are the system calls that are executed by a command
interpreter or shell in order to start a new process?
c. Comment
on the practicability of deadline scheduling.
What are practical problems governing its performance?
d. List three examples of deadlocks that are not
related to a computer system environment.
e. What will happen if page size is changed from
power of 2 to power of 4?
f. What type of operating system is Windows XP?
Describe two of its major features.
g. Describe briefly the Master-Slave,
Symmetric and Floating Supervisor types of the Multiprocessor OS.
Q.2 a.
Consider a logical address space of eight pages of 1024 words each,
mapped onto a physical
memory of 32 frames. How many bits are
there in the logical and physical addresses?
b. Some systems automatically delete all user
files when a user logs off or a job terminates, unless the user explicitly
requests to keep them; other systems keep all files unless the user explicitly
deletes them. Discuss the relative merits of each approach. (2 9)
Q.3 a. For three processes
following parameter values are given below:
Process Arrival Time Burst Time
P1 0.0 8
P2 0.4 4
P3 1.0 1
Using
non preemptive scheduling, find average turnaround time for each process using (i) FCFS
(ii) SJF (iii)
If CPU is left idle for the first 1 unit and then SJF scheduling is
used.
b. Calculate the number of disk accesses needed
to read 20 consecutive logical
blocks
of a file in a system with (i) contiguous allocation (ii) linked allocation
(iii)
indexed allocation. (2 9)
Q.4 a. Describe the differences between logical and physical addresses.
b. What are the differences between user-level
threads and kernel-level threads? Under what circumstances is one type better
than the other? (2 9)
Q.5 a. Suppose that a system is in an unsafe state.
Show that it is possible for the processes to complete their execution without
entering a deadlock state.
b. Using a diagram, carry out an indexed
allocation of a file for a disk based system that has a disk of 30 blocks each
of 1024 bytes (take as a 6×5 matrix), File f1 of 11 logical records of 112 bytes,
File f2 of 890 logical records of 13 bytes, File f3 of 510 bytes of binary data
stream and File f4 of 4 logical records of 95 bytes. (2 9)
Q.6 a. What is the effect of allowing two entries in
a page table to point to the same page frame in memory? How this effect could
be used to decrease the amount of time needed to copy a large of memory from
one place to another? What would be the effect on one page if some bytes of
other page are updated?
b.
An operating system supports paged
virtual memory, using a central processor with a cycle time of 1 ms. It costs
an additional 1 ms to access a page other than the current one. Pages have 1000
words, and the paging device is a drum that rotates at 3000 revolutions per
minute and transfers 1 million words/s. The following statistical measurements
were obtained from the system:
•
1% of all instructions executed accessed a page other than the current page.
•
Of the instructions that accessed another page, 80% accessed a page already that
was in memory.
•
When a new page was required, the replaced page was modified 50% of the time.
Calculate
the effective instruction time on this system, assuming that the system is
running one process only and that the processor is idle during drum transfers. (2
9)
Q.7 a. To build a robust
distributed system, Discuss its three possible types of failure. Which of failures
are also applicable to a centralized system.
b. Assume that there is a page-reference string of
length P for a process with m frames (initially all empty). n distinct
page numbers occur in it. What are the lower and upper bounds number on the number
of page faults. You may use any page
replacement Algorithm. (2 9)