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SPRING 2014,
ASSIGNMENT
PROGRAM-BCA(REVISED
2007)
SEMESTER-3RD SEM
SUBJECT CODE &
NAME-BC0042 – OPERATING SYSTEMS
CREDIT-4
BK ID-B0682
MAX. MARKS-60
Q1. Explain the
Layered Approach. What are the advantages of Layered Approach? 7+3
Answer.
Layered Approach
With proper hardware support,
operating systems can be broken into pieces that are smaller and more
appropriate than those allowed by the original MS-DOS or UNIX systems. The
operating system can then retain much greater control over the computer and
over the applications that make use of that computer. Implementers have more
freedom in changing the inner workings of the system and in creating modular
operating systems. Under the top-
Q2. State
advantages and disadvantages of Threads over multiple processes. [5+5]
Answer.
Advantages and disadvantages
of Threads over multiple processes
Advantages of Threads over
Multiple Processes
·
Context Switching Threads are very inexpensive to create and destroy,
and they are inexpensive to represent. For example, they require space to
store, the PC, the SP, and the general-purpose registers, but they do not
require space to share memory information, Information about open files of I/O
devices in use, etc. With so little context, it is much faster to switch
between threads. In other words, it is relatively
Q3.What are the
different criteria to consider when selecting the "best" scheduling
algorithm? 10
Answer.
Different
criteria to consider when selecting the "best" scheduling algorithm
There are several different
criteria to consider when trying to select the "best" scheduling
algorithm for a particular situation and environment, including:
·
CPU utilization – Ideally the CPU would be busy 100% of the time, so
as to waste 0 CPU cycles. On a real system CPU usage should range from 40%
(lightly loaded) to 90% (heavily loaded.)
·
Throughput –
Number of processes completed per unit time. May range from 10 / second to 1 /
hour
Q4.
What are Semaphores? How can we achieve mutual exclusion using Semaphores? [5+5]
Answer.
Semaphores
A semaphore is a mechanism that
prevents two or more processes from accessing a shared resource simultaneously.
On the railroads a semaphore prevents two trains from crashing on a shared
section of track. On railroads and computers, semaphores are advisory: if a
train engineer doesn't observe and obey it, the semaphore won't prevent a
Q5. What are
Directories? Explain it with respect to DOS and UNIX. [2+4+4]
Answer.
Explanation
Directories with respect to DOS and UNIX
A directory is simply a table
mapping character-string human-readable names to information about files. The
early PC operating system CP/M shows how simple a directory can be. Each entry
contains the name of one file, its owner, size (in blocks) and the block
numbers of 16 blocks of the file. To represent files with more than 16 blocks,
CP/M used multiple directory entries with the same name and different values in
a field called the extent number. CP/M
Q6. Explain the
importance of Direct Memory Access. [10]
Answer.
Importance of
Direct Memory Access
In most mini- and mainframe
computer systems, a great deal of input and output occurs between the disk
system and the processor. It would be very inefficient to perform these
operations directly through the processor; it is much more efficient if such
devices, which can transfer data at a very high rate, place the data directly
into the memory, or take the data directly from the processor without direct
intervention from the processor. I/O performed in this way is usually called direct
memory access, or DMA. The controller for a device employing DMA must have
the capability of generating address signals for the memory, as well as all of
the memory control signals. The processor informs the
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