A protocol is a set of rules that govern data
communication. In networks, communication occurs between the entities in
different systems. Two entities cannot just send bit streams to each other and
expect to be understood. For communication, the entities must agree on a
protocol.
Wednesday, 29 February 2012
Define DNS?
The
Domain Name System (DNS) is a hierarchical naming system built on
a distributed database for computers, services, or any resource connected to
the Internet or a private network. DNS is an Internet service that translates domain names into IP
addresses.
Define TCP/IP?
TCP (Transmission
Control Protocol) is a reliable, point-to-point, connection-oriented,
full-duplex protocol.
Define UDP?
UDP (User Datagram Protocol) is a
connectionless unreliable transport protocol. It extends IP’s host-to-host
delivery service to process-to-process communication service.
Multitasking vs Multithreading:
·
Process is nothing but the program that
is executing.
·
Process based multitasking (or)
multitasking is the feature that allows the system to run two or more programs
concurrently.
·
Example for multitasking: This
multitasking enables us to use the java compiler at the same time when we are
using text editor.
·
Threads are
separate tasks running within a program.
·
In Thread-based multitasking (or)
Multithreading, a single program can execute two or more tasks simultaneously.
·
Example for multithreading: a text
editor can format the text at the same time that it is printing.
·
In multitasking, a program is the
smallest unit of code that can be dispatched by the scheduler.
·
In multithreading, the thread is the
smallest unit of code that can be dispatched by the thread scheduler.
·
The processes in multitasking
(process-based multitasking), are referred to as heavyweight tasks. Since,
o
Each process requires its own separate
address space.
o
Context switching from one process to
another is CPU-intensive task needing more time.
o
Inter-process communication between the
processes is again expensive (as the communication mechanism has to span
separate
·
Multitasking threads cost less in terms
of processor overhead (or) simply Multitasking threads requires less overhead
than multitasking processes because of the following reasons:
o
Multiple threads in a program share the
same address space, and cooperatively share the same heavyweight process.
o
Context switching from one thread to
another is less CPU intensive.
o
Inter-thread communication, is less
expensive (as threads in the program communicate in the same address space).
·
Multithreading are used to write very
efficient programs that make maximum use of CPU, because idle time of the CPU
can be kept down to a minimum.
·
This is really important for the
interactive and networked internet environments.
Eg:-
There may be an instruction in a program
that is reading a file from a different host on the network. Knowing that
reading from a local file system itself is slow compared to the speed of the
CPU, reading from a file on a different host on the network is an even slower
process. In single threaded environment, the rest of the program waits till the
I/O instruction returns. Once the CPU dispatches the I/O instruction it is
free. This idle time of the CPU should be put to good use by executing some
other part of the system.
Multitasking:
·
The process of executing several
programs simultaneously is known as multitasking.
·
Multitasking is further classified as:
o
Process-based multitasking
o
Thread –based multitasking
·
Process-based multitasking usually
referred to as multitasking whereas thread-based multitasking is referred as
multithreading.
Multithreaded Programming
·
A
multithreaded program contains two or more parts that can run concurrently.
Each part of such a program is called a thread.
·
Threads are separate tasks running within a
program.
Need
for Multithreading:
·
Have
you faced the following situations?
o
The
browser cannot skip to the next web page because it is downloading a file?
o
You
cannot enter text into your current document until your word processor completes
the task of saving the document to disk.
·
If the program consists of a single thread, it can
handle only one activity at a time, which results in the above situations.
·
To handle such situations effectively,
multithreaded programming has been developed.
Exception Handling in JAVA:
·
In Java, exception handling is managed via five keywords:
o
Try
o
Catch
o
Throw
o
Throws
o
finally
·
Program statements that should be monitored for exceptions are
contained within a try block.
·
If an exception occurs within the try block, it is thrown. The exception which is thrown should be
caught by the code (using catch)
and that should also be handled.
·
System-generated exceptions are automatically thrown by the Java
run-time system. To manually throw an exception, use the keyword throw.
·
Any exception that is thrown out of a method must be specified
as such by a throws clause.
·
Any code that absolutely
must be executed before a method returns is put in a finally block.
This
is the general form of an exception-handling block:
try
{
// block of code to
monitor for errors
}
catch (ExceptionType1 exOb)
{
// exception
handler for ExceptionType1
}
catch (ExceptionType2 exOb)
{
// exception
handler for ExceptionType2
}
// ...
finally
{
// block of code to
be executed before try block ends
}
· Exception Type is the type of exception that has occurred.
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