Pc Hardware

PComputer network
A computer network is simply two or more computers connected together so they can exchange information. A small network can be as simple as two computers linked together by a single cable. This course introduces you to the hardware and software needed for a network, and explains how a small network is different from larger networks and the Internet. Most networks use hubs to connect computers together. A large network may connect thousands of computers and other devices together. A wireless network connects computers without a hub or network cables but use radio communications to send data between each other. Networking allows you to share resources among a group of computer users. If you have a printer connected to your computer, you can share the printer with other computers on the network. Then instead of buying a printer for every computer, all the computers can print across the network to the printer. If you already have access to the Internet from one computer on your network, you can share that Internet connection with other computers on the network. Then all the computers on your network can browse the Web at the same time, using this single Internet connection.
Protocol
A standard set of regulations and requirements that allow two electronic items to connect to and exchange information with one another. Protocols regulate data transmission among devices as well as within a network of linked devices through both error control and specifying which data compression method to use. In particular, protocols decide: the method of error checking, how to compact data (if required), how the transmitting device signals that it has concluded sending data, and how the receiving device signals that it has completed receiving data. Among the most common Internet protocols are FTP (File Transfer Protocol), HTTP (Hypertext Transfer Protocol), TCP/IP (Transfer Control Protocol/Internet Protocol), and SMTP (Simple Mail Transfer Protocol). In other word, a uniform set of rules that enable two devices to connect and transmit data to one another. Protocols determine how data are transmitted between computing devices and over networks. They define issues such as error control and data compression methods. The protocol determines the following: type of error checking to be used data compression method (if any), how the sending device will indicate that it has finished a message and how the receiving device will indicate that it has received the message. Internet protocols include TCP/IP (Transfer Control Protocol/Internet Protocol), HTTP (Hypertext Transfer Protocol), FTP (File Transfer Protocol), and SMTP (Simple Mail Transfer Protocol).

PPP (Point-to-Point Protocol)
PPP (Point-to-Point Protocol) is a protocol for communication between two computers using a serial interface, typically a personal computer connected by phone line to a server. For example, your Internet server provider may provide you with a PPP connection so that the provider's server can respond to your requests, pass them on to the Internet, and forward your requested Internet responses back to you. PPP uses the Internet protocol (IP) (and is designed to handle others). It is sometimes considered a member of the TCP/IP suite of protocols. Relative to the Open Systems Interconnection (OSI) reference model, PPP provides layer 2 (data-link layer) services. Essentially, it packages your computer's TCP/IP packets and forwards them to the server where they can actually be put on the Internet.
PPP is a full-duplex protocol that can be used on various physical media, including twisted pair or fiber optic lines or satellite transmission. It uses a variation of High Speed Data Link Control (HDLC) for packet encapsulation.
PPP is usually preferred over the earlier de facto standard Serial Line Internet Protocol (SLIP) because it can handle synchronous as well as asynchronous communication. PPP can share a line with other users and it has error detection that SLIP lacks. Where a choice is possible, PPP is preferred.
Local area network (LAN)
A local area network (LAN) is a group of computers and associated devices that share a common communications line or wireless link. Typically, connected devices share the resources of a single processor or server within a small geographic area (for example, within an office building). Usually, the server has applications and data storage that are shared in common by multiple computer users. A local area network may serve as few as two or three users (for example, in a home network) or as many as thousands of users (for example, in an FDDI network).
Major local area network technologies are: Ethernet Token Ring FDDI Ethernet is by far the most commonly used LAN technology. A number of corporations use the Token Ring technology. FDDI is sometimes used as a backbone LAN interconnecting Ethernet or Token Ring LANs. Another LAN technology, ARCNET, once the most commonly installed LAN technology, is still used in the industrial automation industry.
Typically, a suite of application programs can be kept on the LAN server. Users who need an application frequently can download it once and then run it from their local hard disk. Users can order printing and other services as needed through applications run on the LAN server. A user can share files with others at the LAN server; read and write access is maintained by a LAN administrator. A LAN server may also be used as a Web server if safeguards are taken to secure internal applications and data from outside access.
Metropolitan area network (MAN)
A metropolitan area network (MAN) is a network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN). The term is applied to the interconnection of networks in a city into a single larger network (which may then also offer efficient connection to a wide area network). It is also used to mean the interconnection of several local area networks by bridging them with backbone lines. The latter usage is also sometimes referred to as a campus network.
Examples of metropolitan area networks of various sizes can be found in the metropolitan areas of London, England; Lodz, Poland; and Geneva, Switzerland. Large universities also sometimes use the term to describe their networks. A recent trend is the installation of wireless MANs.
WAN (Wide Area Network)
A wide area network (WAN) is a geographically dispersed telecommunications network. The term distinguishes a broader telecommunication structure from a local area network (LAN). A wide area network may be privately owned or rented, but the term usually connotes the inclusion of public (shared user) networks. An intermediate form of network in terms of geography is a metropolitan area network (MAN).
Internetworks
Internetworking is a term used by Cisco, BBN, and other providers of network products and services as a comprehensive term for all the concepts, technologies, and generic devices that allow people and their computers to communicate across different kinds of networks. For example, someone at a computer on a token ring local area network may want to communicate with someone at a computer on an Ethernet local area network in another country using a wide area network interconnection. The common internetwork protocols, routing tables, and related network devices required to achieve this communication constitute internetworking.
The standard reference model for internetworking is Open Systems Interconnection (OSI), which could also be used as a model for intranetworking as well. OSI enables any technology to be related to another technology because each can be related to the standard communication model. OSI provides a layering approach to the problem of exchanging data across a network or a network of networks so that the problem can be broken down into easier-to-understand components and so that boundaries between components can be more easily determined.

IP address (Internet Protocol Address)
The Internet Protocol (IP) is the method or protocol by which data is sent from one computer to another on the Internet. Each computer (known as a host) on the Internet has at least one IP address that uniquely identifies it from all other computers on the Internet.
When you send or receive data (for example, an e-mail note or a Web page), the message gets divided into little chunks called packets. Each of these packets contains both the sender's Internet address and the receiver's address. Any packet is sent first to a gateway computer that understands a small part of the Internet. The gateway computer reads the destination address and forwards the packet to an adjacent gateway that in turn reads the destination address and so forth across the Internet until one gateway recognizes the packet as belonging to a computer within its immediate neighborhood or domain. That gateway then forwards the packet directly to the computer whose address is specified.
Because a message is divided into a number of packets, each packet can, if necessary, be sent by a different route across the Internet. Packets can arrive in a different order than the order they were sent in. The Internet Protocol just delivers them. It's up to another protocol, the Transmission Control Protocol (TCP) to put them back in the right order.
IP is a connectionless protocol, which means that there is no continuing connection between the end points that are communicating. Each packet that travels through the Internet is treated as an independent unit of data without any relation to any other unit of data. (The reason the packets do get put in the right order is because of TCP, the connection-oriented protocol that keeps track of the packet sequence in a message.) In the Open Systems Interconnection (OSI) communication model, IP is in layer 3, the Networking Layer.
The most widely used version of IP today is Internet Protocol Version 4 (IPv4). However, IP Version 6 (IPv6) is also beginning to be supported. IPv6 provides for much longer addresses and therefore for the possibility of many more Internet users. IPv6 includes the capabilities of IPv4 and any server that can support IPv6 packets can also support IPv4 packets.

Network topology
In communication networks, a topology is a usually schematic description of the arrangement of a network, including its nodes and connecting lines. There are two ways of defining network geometry: the physical topology and the logical (or signal) topology.
The physical topology of a network is the actual geometric layout of workstations. There are several common physical topologies, as described below and as shown in the illustration.

In the bus network topology, every workstation is connected to a main cable called the bus. Therefore, in effect, each workstation is directly connected to every other workstation in the network.
In the star network topology, there is a central computer or server to which all the workstations are directly connected. Every workstation is indirectly connected to every other through the central computer.
In the ring network topology, the workstations are connected in a closed loop configuration. Adjacent pairs of workstations are directly connected. Other pairs of workstations are indirectly connected, the data passing through one or more intermediate nodes.
If a Token Ring protocol is used in a star or ring topology, the signal travels in only one direction, carried by a so-called token from node to node.
The mesh network topology employs either of two schemes, called full mesh and partial mesh. In the full mesh topology, each workstation is connected directly to each of the others. In the partial mesh topology, some workstations are connected to all the others, and some are connected only to those other nodes with which they exchange the most data.
The tree network topology uses two or more star networks connected together. The central computers of the star networks are connected to a main bus. Thus, a tree network is a bus network of star networks.
Logical (or signal) topology refers to the nature of the paths the signals follow from node to node. In many instances, the logical topology is the same as the physical topology. But this is not always the case. For example, some networks are physically laid out in a star configuration, but they operate logically as bus or ring networks.
Transmission Mode
A transmission mode describes the manner in which a communication between a sender and a receiver can take place. The following modes are defined: Simplex: Communication goes in one direction only, and the sender can use the entire communication channel. A ticker-tape machine is an example. Half-duplex: Communication can go in both directions, but in only one direction at a time. The sender can use the entire channel. In order to change direction, a special signal must be given and acknowledged. The time required to turn over control to the other side is called the line turnaround (or just turnaround) time. Turnaround time can become significant in certain transmissions. A CB connection is an example. Full-duplex: Communication can go in both directions simultaneously, but each part gets to use only half the channel. Modem connections are an example. Echo-plex: An error-checking mode in which characters typed for transmission are sent back to the screen from the receiver to permit direct comparison with what was typed. *Transmission modes can be divided into two fundamental categories:
• Serial - one bit is sent at a time
-Serial transmission is further categorized according to timing of transmissions
• Parallel - multiple bits are sent at the same time