ALCCS
FEBRUARY 2009
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
x 4)
a. Discuss the two models of interprocess communication
highlighting their strengths and weaknesses
b. Discuss file storage in
MS-DOS. Calculate the number of entries required in the FAT table given these
parameters: Disk capacity-30Mbyte, Block size-512 bytes, Blocks/cluster-2.
c. Explain what is
multi-level scheduling.
d. Discuss the
various implications of assigning a new timestamp to a transaction that is
rolled back. Also discuss how the system
process transactions that were issued after the rolled-back transaction but
having timestamps smaller than the new timestamp of the rolled back
transaction.
e. Explain the
concept of virtual memory system with an example.
f. Discuss the
memory organization of buddy system with its merits and demerits.
g. Briefly discuss Network OS, Multiprocessor OS, and
Distributed OS.
Q.2 a. Following is the snapshot of a CPU
Process CPU Burst Arrival
Time
P1 10 0
P2 29 1
P3 03 2
P4 07 3
Draw the Gantt chart and calculate the turnaround
time and waiting time of the jobs for FCFS (First Come First Served), SJF
(Shortest Job First), SRTF (Shortest Remaining Time First) and RR (Round Robin
with time quantum 10) scheduling algorithms. Arrival Time is only applicable to
SRTF algorithm.
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 x 9)
Q.3 a. Consider
a system consisting of ‘m’ resources of the same type being shared by ‘n’
processes. Resources can be requested
and released by processes only one at a time.
Show that the system is deadlock free if the two conditions hold
(i)
The maximum need of each process is between 1 & m resources.
(ii) The sum
of all maximum needs is less than m+n.
b. Round
robin schedulers normally maintain a list of all runnable processes, with each
process occurring exactly once in the list. What would happen if a process
occurred twice in the list? Can you think of any reason for allowing this? (2 x 9)
Q.4 a. In a paged segmented system, a virtual address consists of 32 bits
of which 12 bits are a displacement, 11 bits are a segment number and 9 bits
are a page number. Calculate (i) page size (ii) maximum segment size (iii)
maximum number of pages (iv) maximum number of segments.
b. Explain the Symbolic address, Relocatable
address, Absolute address in memory management with an example. (2 x 9)
Q.5 a. Why the interrupt disable method to achieve
mutual exclusion does not work for multiprocessor system? Explain.
b. Using a diagram, show how an indexed
allocation of a file may be done for a disk based system with the following
characteristics?
(i)
A
System has a disk of 30 blocks each of 1024 bytes (may be modeled as a 6×5
matrix).
(ii)
File
f1 of 11 logical records of 112 bytes
(iii)
File
f2 of 890 logical records of 13 bytes
(iv)
File
f3 of 510 bytes of binary data stream
(v)
File
f4 of 4 logical records of 95 bytes (6+12)
Q.6 a. How do system calls differ from ordinary
library routines, as both are supplied by the language?
b. Describe using a diagram how a logical address
consisting of 24 bits could be converted to a segment address supporting upto
256 segments. What would be the maximum size of each segment? (2 x 9)
Q.7 a. Explain the concept of transaction atomicity. Where
transaction atomicity is applicable in OS?
b. Suppose that a disk drive has 5000 cylinders,
0 to 4999. The drive is currently serving a request at cylinder 143, and the
previous request was at cylinder 125. The queue of pending request in FIFO order
is 86, 1470, 913, 1774, 948, 1509, 1022, 1750, 130. Calculate the total
distance (in terms of cylinder), starting from current head position, for the
following disk scheduling algorithms. (a) FCFS (b) SSTF (c) SCAN (d) C-SCAN. (2
x 9)