Fall 2014 - Scheme of Evaluation
PROGRAM
SEMESTER
SUBJECT CODE &
NAME
CREDIT
BK ID
MAX. MARKS
Q.No
1
A
4
B1405
60
Question and Scheme of Evaluation
Differentiate between Distributed Systems and Real-time Systems.
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MCA(REVISED FALL 2012)
SECOND
MCA2010 – OPERATING SYSTEM
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5+5
10
In distributed system, all the computations are distributed among
several processors. Distributed systems are also referred as
loosely coupled systems because here the processors do not
share memory or a clock. Instead, each processor has its own
local memory. The processors communicate with one another
through various communication lines, such as high speed buses
or telephone lines. The processors in distributed system vary in
size, function and are referred as sites, nodes, and computers
and so on depending on the context in which they are
mentioned.
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10
Real-time operating systems are specially designed to respond
to events that happen in real time. A real time operating system
has well-defined, fixed time constrains. Processing must be
done within the defined constraints, or else the system will fail.
This feature is very useful in implementing systems such as an
airline reservation system. In such a system, the response time
should be very short because a customer’s reservation is to be
done while he/she waits.
There are two flavors of real-time systems. A hard real-time
system guarantees that critical tasks complete at a specified
time. A less restrictive type of real time system is soft real time
system, where a critical real time task gets priority over other
tasks, and remains that priority until it completes.
Explain the different process states.
A process being an active entity, changes state as execution
proceeds. A process can be any one of the following states:
 New: Process being created.
 Running: Instructions being executed.
 Waiting (Blocked): Process waiting for an event to occur.
 Ready: Process waiting for CPU.
 Terminated: Process has finished execution.
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10
3
Define Deadlock. Explain necessary conditions for deadlock.
A
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Deadlock occurs when we have a set of processes [not
necessarily all the processes in the system], each holding some
resources, each requesting some resources, and none of them
is able to obtain what it needs, i.e. to make progress.
A deadlock occurs in a system if the following four conditions
hold simultaneously:
1) Mutual exclusion: At least one of the resources is nonsharable, that is, only one process at a time can use the
resource.
2) Hold and wait: A process exists that is holding on to at least
one resource and waiting for an additional resource held by
another process.
3) No preemption: Resources cannot be preempted, that is, a
resource is released only by the process that is holding it.
4) Circular wait: There exist a set of processes P 0, P1… Pn of
waiting processes such that P0 is waiting for a resource held by
P1, P1 is waiting for a resource held by P 2… Pn-1 is waiting for a
resource held Pn and Pn is in turn waiting for a resource held by
P0.
Differentiate between Sequential access and Direct access
methods.

In Sequential access method, information in a file is accessed
sequentially one record after another. To process the ith record
all the i-1 records previous to i must be accessed. Sequential
access is based on the tape model that is inherently a
sequential access device. Sequential access is best suited
where most of the records in a file are to be processed. For
example, transaction files.
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Sometimes it is not necessary to process every record in a file.
It may not be necessary to process records in the order in
which they are present. Information present in a record of a file
is to be accessed only if some key value in that record is
known. In all such cases, direct access is used. Direct access
is based on the disk that is a direct access device and allows
random access of any file block. Since a file is a collection of
physical blocks, any block and hence the records in that block
are accessed. For example, master files.
Differentiate between Daisy chain bus arbitration and Priority
encoded bus arbitration.
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Daisy chain arbitration: Here, the requesting device or devices
assert the signal bus_request. The bus arbiter returns the
bus_grant signal, which passes through each of the devices
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which can have access to the bus. Here, the priority of a device
depends solely on its position in the daisy chain. If two or more
devices request the bus at the same time, the highest priority
device is granted the bus first, and then the bus_grant signal is
passed further down the chain. Generally a third signal
(bus_release) is used to indicate to the bus arbiter that the first
device has finished its use of the bus. Holding bus_request
asserted indicates that another device wants to use the bus.
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6
A
5
Priority encoded arbitration: Here, each device has a request
line connected to a centralized arbiter that determines which
device will be granted access to the bus. The order may be
fixed by the order of connection (priority encoded), or it may be
determined by some algorithm preloaded into the arbiter.
Following figure shows this type of system. Note that each
device has a separate line to the bus arbiter.
Differentiate between encryption and decryption. What are the two
basic methods for encryption?
Encryption is an important tool in protection, security and
authentication. The process involves two steps

Encryption: the original message is changed to some other
form
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
Decryption: the encrypted message is restored back to the
original.
10
Encryption could be by one of the following two basic methods:
 Transposition ciphers
 Substitution ciphers
5
In transposition ciphers the contents of the data are not changed but
the order is changed. For example, a message could be sent in
reverse order like:
I am fine  enif ma I
Substitution ciphers work by sending a set of characters different
from the original like:
I am fine  r zn ormv
*A-Answer
Note –Please provide keywords, short answer, specific terms, and specific examples (wherever necessary)
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