Complete Computer Knowledge Portal

Sunday, March 31, 2013

RAID (Redundant Array of independent disks)

RAID (Redundant Array of independent disks) or Redundant Array of Inexpensive Disks is a storage technology that combines multiple disk drive components into a logical unit.The main purpose of RAID is fault tolerance and get better performance.This Technique is generally used in servers where huge and important data is saved.
RAID uses number of standard schemes which are referred as levels.These levels and their associated data formats are standardized by the Storage Networking Industry Association (SNIA) in the Common RAID Disk Drive Format (DDF) standard.

RAID0(Disk Stripping)

in RAID 0 data is split  into blocks that get written across all the drives in the array.e.g instead of writing a 500MB file to one disk ,it simultaneously  write 125MB to each of four different disks(if disks are five than 100MB each), offering superior I/O performance but no fault tolerance. This performance is enhanced by multiple disk controllers.Failure in any disk destroys the array.

How to Change MAC Address

Media Access Control Address(MAC address)
STEP1–>Click start

STEP2–>Control panel

Difference Between LAN,MAN and WAN

Local Area Network
Metropolitan Area Network
Wide Area Network
Less Costly
More Costly
Up to 10-100Mbps
256Kbps to 2Mbps
Up to 50 Kms.
Up to 10,000 Kms.
Bus and Ring
Distributed Queue
Dual Bus [DQDB]
ATM, Frame Relay,
Location of computers
connected in the
Computers are located
within the same
Computers are
located in the city
and are connected
using modems or
telephone lines so
that they can be
easily connected with
Each other.
Computers are
distributed all over
the country or the
Continent. The
connection is made
via satellite
communication link
Or via internet.


Local Area Network(LAN)

It is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building using network media.
ARCNET, Token Ring and other technology standards have been used in the past, but Ethernet over twisted pair cabling, and Wi-Fi are the two most common technologies currently used to build LANs.

LAN is generally limited to specific geographical area less than 2 K.M., supporting high speed networks. A wide variety of LANs have been built and installed, but a few types have more recently become dominant. The most widely used LAN system is the Ethernet system based on the bus topology.
Intermediate nodes (i.e., repeaters, bridges and switches) allow to be connected together to from larger LANs. A LAN may also be connected to another LAN or to WANs and MANs using a “router” device.

There are essentially five components of a LAN:
1) Network devices such as Workstations, printers, file servers which are
normally accessed by all other computers.
2) Network Communication Devices i.e., devices such as hubs, routers, switches etc. used for network connectivity.
3) Network Interface Cards (NICs) for each network device required to access the network. It is the interface between the machine and the physical network.
4) Cable as a physical transmission medium.
5) Network Operating System –software applications required to control the use of network operation and administration.

OSI Model

Open System Interconnection is a standard that describes how message  is transmitted and received between two points in telecommunication.It is developed by ISO( International Organization for Standardization ). It is a seven layer model and are labeled 1 to 7 with layer 1 at bottom(as per X.200 Recommendations).This concept of a seven-layer model was provided by the work of Charles Bachman, Honeywell Information Services.Idea behind this model was that the telecommunication between two points can be divided into layers with each layer adding its own set of special, related functions. The seven Layers are: 1)Physical Layer 2)Data Link Layer 3)Network Layer 4)Transport Layer 5)Session Layer 6)Presentation Layer 7)Application Layer. these seven layers are divided into two groups. The upper four layers are used whenever a message passes from or to a user(known as Host Layers). The lower three layers (up to the network layer) are used when any message passes through the host computer(known as Media Layers) . Messages intended for this computer pass to the upper layers. Messages destined for some other host are not passed up to the upper layers but are forwarded to another host.

How to Configure Outlook Account

Here are the some simple steps to configure outlook account in Outlook 2010

STEP1–>Click Start –> Control Panel–> Mail

STEP2–>Click add Button

Network Topology

Network Topology is the arrangement of computers or nodes in the describes how nodes are connected to each other in a network.There are two basic categories of network topologies:
i)Physical topologies
ii)Logical topologies
Physical Topologies:-The shape of the cabling layout used to link devices  in any network is referred to as physical topology of the network. This refers to the layout of cabling, the locations of nodes, and the interconnections between the nodes and the cabling.
Logical Topologies:-It is the way by which signals act on the network media, or  data passes through the network from one device to the next without regard to the physical interconnection of the devices.
Various Physical Topologies are:

Simplex, Half Duplex,Full Duplex

It is the mode of transmission in which data is transmitted in one way only.The transmitter will always transmit signal and receiver will always work as receiver and can’t be used as transmitter.This method is not often used because it is not possible to send back error or control signals to the transmit end.
Best example of Simplex mode of transmission is,data transmission from keyboard to mouse.

Saturday, March 30, 2013

Peer to Peer and Client Server Model

Client Server Model
Client Server model is a Networking Technique in which one of two roles are assigned  to the computers in a network: Client or server.server is a computer system that selectively shares its resources and provide services to its clients; client is a computer that make use of a resources with the help of server. Some features of this model are:
1)There will be atleast one Server and any no. of clients.
2)Server Provides services to if client 1 wants to access internet,then it will make request to server.server will check its rights and will provide access to internet as per rights assigned.Similarly if anybody wants to communicate with client 1 ,then it will authorized by server to gain access.
3)There is centralized controlling hub hence more security and rights assignment can be implemented.
4)Failure of Server will fail the entire network.
5)Clients and servers exchange messages in a request-response messaging pattern: The client sends a request, and the server returns a response.

below given image demonstrates the complete Client server model.


Telnet is a networking protocol that is used on the Internet or LAN  to provide a bidirectional interactive Command line  communication facility using a virtual terminal connection.Telnet was originally designed for the small institutions and security was not the concern.Telnet, by default, does not encrypt any data sent over the connection including passwords.The Telnet protocol uses various commands to control the client-server connection. These commands are transmitted within the data stream. The commands are distinguished from the data by setting the most significant bit to 1. (Remember that data is transmitted as 7-bits with the eighth bit set to 0) Commands are always introduced by the Interpret as command (IAC) character.
Communication is established using TCP/IP and is based on a Network Virtual Terminal (NVT). On the client, the Telnet program is responsible for translating incoming NVT codes to codes understood by the client’s display device as well as for translating client-generated keyboard codes into outgoing NVT codes.
The NVT uses 7-bit codes for characters. The display device, referred to as a printer in the RFC, is only required to display the standard printing ASCII characters represented by 7-bit codes and to recognize and process certain control codes. The 7-bit characters are transmitted as 8-bit bytes with the most significant bit set to zero. An end-of-line is transmitted as a carriage return (CR) followed by a line feed (LF). If you want to transmit an actual carriage return, this is transmitted as a carriage return followed by a NUL (all bits zero) character.

Dot Matrix Printer

Dot Matrix Printers(DMP) are impact Printers and make use of Print head for the printing. Print head strikes an ink-soaked cloth ribbon against the paper,to generate text or is similar to type writer but the difference is that in typewriter each font uses its own striker whereas in DMP same print head performs this by using matrix pattern.
Working Principle: Printer head Moves in horizontal direction.Print Head controller controls it by sending electrical signals which forces the appropriate wires to strike against the inked ribbon, making dots on the paper and forming the desired characters. below given clearly illustrates this.

Proxy Server

In Computer Networks,Proxy Server is a Server that acts as intermediary for requests from clients seeking resources from other servers.A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource available from a different server and the proxy server evaluates the request as a way to simplify and control its complexity.
Uses of Proxy

1)High Security because each client is provided access according to rights assigned to him.
2)To Speed up access to resources.these are used to cache web pages from web servers which makes fast access.
3)To create Web logs for the audit usage.
4)To scan transmitted content for malware before delivery
5)Access enhancement/restriction
6)Filtering of data means which contents can be accessed or not.
Types of Proxy

Difference Between DDR,DDR2 and DDR3 RAM

Bus Clock(MHz)
Internal Rate(MHz)
Prefetch (Min. Fetch)
Operating Voltage
Micro DIMM Pins
Transfer Rate(MT/s)

Difference Between Hardware and Software

All the Physical Units of Computer System to whom we can touch and feel are Hardware.
Software is a collection of  Programs and related data that provides the instructions for telling a computer what to do and how to do it.
Hardware is actual components that your computer is made of: RAM, ROM, Motherboard, modem, wireless chips etc.
Software is any Program that you can load onto Operating System (Windows, Linux) or games or any other applications.

Difference Between Volatile and Non-Volatile Memory

Volatile Memory
Non-Volatile Memory
Volatile memory is computer memory that requires power to maintain the stored information.
Non-volatile storage is computer memory that can retain stored
information even when not powered
Volatile memory retains the information as long as power supply is on, but when power supply is off or interrupted the stored memory is lost. Therefore it is used for temporary storage.
Non-volatile memory is typically used for the task of secondary storage, or long-term persistent storage.

Difference Between Computer and Calculator

Sr. No.
A computer is an electronic device which can performs each and every task at a very high speed and high accuracy.
It is also an electronics device but it can do calculation work only.
A computer can work with numbers and words both.
A calculator can work only with numbers.
A computer can store large volume of data in its memory and reproduce any part of it, as and when needed
A calculator is not capable of storing data for long duration.

Difference Between Application Software and System Software

Sr. No.
Application Software
System Software
Application Software are those Software which are designed to help the user to perform specific tasks.
System Software is Computer Software which manages and controls computer hardware so that application software can perform tasks.
Application Software is installed according to the requirements of the user.
System Software is gets installed when the operating system is installed on the computer.
Application Software includes Media Players, Word Processors and
Spread Sheet Programs.
System Software Includes programs such as compilers, debuggers, drivers, assemblers.

Difference Between C and C++

Sr. No.
C Language
C++ Language
C is a procedural programming Language.
C++ is a multi-paradigm
language which means it is procedural as well as object
oriented language.
In C, importance is given to the steps or procedure of the program.
C++ focuses on the data rather than the process.
Data is not secure because oops feature such as data hiding etc. are not present in C.
Data is secure because it supports oops concepts.
C is a low-level Language.
It is Middle level Language.
C uses the top-down approach .Program is formulated step by step,
each step is processed into detail.
C++ uses the bottom-up approach. In C++ base elements are first formulated which then are linked together to give rise to larger systems.

Difference Between Compiler and Interpreter

Sr. No.
Compiler is used to translate high level instruction into machine language.
Interpreter is used to translate the high level instruction into an
intermediate code.
The compiler executes the entire program at a time.
The interpreter executes each and every line of program individually.
Compiler reports errors at the end of program compilation.
An interpreter reports error at the end of each line compilation and does not move to next line until this error is not removed.

Difference Between Top Down and Bottom Up Approach

Sr. No.
Top-Down Approach
Bottom-Up Approach
In this approach an overview of the system is first formulated, specifying but not detailing any first-level subsystems. Each Subsystem is then refined in yet greater detail,sometimes in many additional subsystem levels, until the entire specification is reduced to base elements.In this approach the individual base elements of the system are first Specified in great detail. These elements are then linked together to form larger subsystems, which then in turn are linked, sometimes in many levels, until a complete top-level System is formed.
This Approach is used in the development of brand new systems.This approach is used in existing Systems.
Top down design begins the design with the main or top-level module, and progresses downward to the lowest level modules or subsystems.Bottom up design begins the design with the lowest level modules or subsystems, and Progresses upward to the main program, module, or subsystem.

Difference Between Local and Global Variables

Sr. No.
Local Variable
Global Variable
Local variables are those variables which are accessible inside the specific function that creates them.
Global Variables are those variables that can be accessed by any function comprising the program.
They are normally implemented using a stack.
They are implemented by associating memory locations with variable names.
They are recreated each time a function is executed or called.
They do not get recreated if the function is recalled.

Difference Between Stack and Queue

Stack is a data structure in which elements are added and removed from only one end, which is called the top.
A queue is a data structure in which elements are added from one end (from back) and are removed from another end (from front).
In Stack only two operations are allowed: PUSH (to add elements),
PULL (to remove  elements).
Queue uses two operations are: ENQUEUE (to add elements), DEQUEUE (to remove elements).
It Works on LIFO (Last in first out principle).
It works on FIFO (first in first out principle).