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.
Wednesday, 29 February 2012
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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