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

Difference Between LAN,MAN and WAN

Characteristics	LAN	MAN	WAN
Acronym	Local Area Network	Metropolitan Area Network	Wide Area Network
Cost	Less Costly	More Costly	Costliest
Speed	Up to 10-100Mbps	5-10Mbps	256Kbps to 2Mbps
Range	1Km	Up to 50 Kms.	Up to 10,000 Kms.
Topology	Bus and Ring	Distributed Queue Dual Bus [DQDB]	ATM, Frame Relay, Sonnet
Location of computers connected in the system	Computers are located within the same Building.	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.

LAN,MAN and WAN

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

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

Network Topology

Network Topology is the arrangement of computers or nodes in the network.it 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:

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 clients.eg. 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.

Difference Between Hub Switch and Router

Hub	Switch	Router
In Hub signal introduced at the input of any port appears at the output of every port except the original  incoming. The device is a form of multiport repeater.	Network switch is a telecommunication device which receives a  message from any device connected to it and then transmits the message only to the device for which the message was meant. This makes the switch a more intelligent device than a hub	A router looks at packet headers to determine which port it needs to forward a packet through, and also will translate packets between different protocols if needed. A router can also define subnets and will filter traffic as needed. Routers usually include DHCP, port forwarding capabilities and a whole host of other things usually controlled by software and therefore user customizable.
A Hub is, in its simplest form, just like a mains multi plug unit. There is no intelligence or circuitry in it. More complex units may incorporate an amplifier or repeater. The network signal goes into one port and out of all the others.	A Switch has a small level of intelligence, in that it can open a message, check the IP address, and direct the message packets to the port on which the device with that IP address resides. It cannot modify IP addresses or see addresses outside of the range of the ‘home’ network	A Router can read IP addresses, and direct the messages to another network with different IP addresses to the originating network. The Router software can build up an address table, so that it ‘knows’ where other devices are.

Difference Between Synchronous and Asynchronous Transmission

Sr. No.	Synchronous Transmission	Asynchronous Transmission
1	Synchronous data transmission is a data transfer method in which a continuous stream of data signals is accompanied by timing signals (generated by an electronic clock) to ensure that the transmitter and the receiver are in step (synchronized) with one another. The data is sent in blocks (called frames or packets) spaced by fixed time intervals.	In contrast, asynchronous transmission works in spurts and must insert a start bit before each data character and a stop bit at its termination to inform the receiver where it begins and ends. The term asynchronous is used to describe the process where transmitted data is encoded with start and stop bits, specifying the beginning and end of each character.
2	It uses start and stop frames.	It uses start and stop bits.
3	Synchronous Transmission sends packets of characters at a time. Each packet is preceded by a Start Frame. This Start Frame is used to tell the receiving station that a new packet of characters is arriving, and it   synchronizes the receiving station’s internal clock. The packets also have End Frames to indicate the end of the packet.	Asynchronous Transmission sends only 1 character at a time. A character can be a letter of the alphabet, a  number or a control character. Preceding each character is a Start bit and ending each character is 1 or more Stop bits.

Difference Between RISC and CISC

No.	RISC	CISC
1	It is an acronym for Reduced Instruction Set Computer. It is a type of microprocessor that has been designed to carry out few instructions at the same time.	CISC stands for Complex Instruction Set Computer. It is actually a CPU which is capable of executing many operations through a single instruction.
2	Faster than CISC	Slower than RISC chips when performing instructions
3	Pipelining can be implemented easily	Pipelining implementation is not easy
4	Direct addition is not possible	Direct addition between data in two memory locations. Ex.8085
5	Simple, single-cycle instructions that perform only basic Functions. Assembler instructions correspond to microcode instructions on CISC machine	A large and varied instruction set that includes simple, fast instructions for performing basic tasks, as well as complex, multi cycle Instructions that correspond to statements in an HLL.
6	RISC architecture is not widely used	At least 75% of the processor use CISC architecture
7	RISC chips require fewer transistors and cheaper to produce. Finally, it’s easier to write powerful optimized compilers	In common CISC chips are relatively slow (compared to RISC chips) per instruction, but use little (less than RISC) instructions.
8	RISC puts a greater burden on the software. Software developers need to write more lines for the same tasks	In CISC, software developers no need to write more lines for the same tasks

Database Normalization

Database Normalization is the process of organizing data in a database by eliminating redundancy and inconsistent dependency. it divides large tables into smaller tables ,which are less redundant , and defines relationships between them.The Main motive is to isolate data so that additions, deletions, and modifications of a field is made in just one table and then propagated through the rest of the database using the defined relationships.

Database normalization uses few rules . Each rule is called a “normal form.” If the first rule is observed, the database is said to be in “first normal form.” If the first three rules are observed, the database is considered to be in “third normal form.” Although other levels of normalization are possible, third normal form is considered the highest level necessary for most applications.

Normalization Form	Description	Example
First normal form (1NF)	It is a property of a relation in a relational database. A relation is in first normal form if the domain of each attribute contains only atomic values, and the value of each attribute contains only a single value from that domain	For example, to track an inventory item that may come from two possible sources, an inventory record may contain fields for Vendor Code 1 and Vendor Code 2.

File Transfer Protocol(FTP)

File Transfer Protocol(FTP) is Networking Protocol that is used to transfer files from one host to another host based on TCP/IP Network.It Completely works on client server model and make use of separate data and control lines between server and client.User Requires username and password to connect or it may connect anonymously if  server is configured to do so.FTP is not able to encrypt its traffic; all transmissions are in clear text, and usernames, passwords, commands and data can be easily read by anyone able to perform packet capture.
This Protocol is totally transaction oriented.A transaction is defined to be an entity of information communicated between cooperating processes.Transaction has three fields:
1)72 bit Descriptor Field
2)Variable Length Data Field(Including Zero)
3)Variable length Filler Field
Hence,Transaction Length=(72 + data + filler) bits.

<Code> :This field has three 8 bit bytes. The first byte is interpreted as transaction type, the second byte as data type and the third byte as extension of data type.

Transmission Control Protocol(TCP)

Transmission Control Protocol(TCP) is a connection-oriented, end-to-end reliable protocol designed to fit into a layered hierarchy of protocols which support multi-network applications.the primary purpose of the TCP is to provide reliable, securable logical circuit or connection service between pairs of nodes.
following are some functions that are performed by TCP–>
i)Basic Data Transfer:-TCP is responsible to transfer a continuous stream of octets in each direction between its users by packaging some number of octets into segments for transmission through the internet system. TCPs decide when to block and forward data at their own convenience.
ii)Reliability:-The TCP  recovers data that is damaged, lost, duplicated, or delivered out of order by the internet communication system. To do so a sequence number to each octet transmitted, and requiring a positive acknowledgment (ACK) from the receiving TCP. If the ACK is not received within a timeout interval, the data is retransmitted. At the receiver, the sequence numbers are used to correctly order segments that may be received out of order and to eliminate duplicates. Damage is handled by adding a checksum to each segment transmitted, checking it at the receiver, and discarding damaged segments.