A very important component of an informative system is the trasmition of information. In the software design are used the networks for it. There are two principal types of network: WAN and LAN. A wide-area network (WAN) is a network of geographically distant computers and terminals. In business a personal computer sending data any significant distance is probably sending it to a minicomputer or mainframe computer. Since these larger host computers are designed to be accessed by terminals, a personal computer can access a minicomputer or a mainframe only if it uses special software called 'emulation software' to imitate, or emulate, a terminal. That is, the larger computer must consider the personal computer as just another terminal. Special comunications software permits downloading - retrieving files from the host computer - or uploading - sending files from a personal computer to the host computer. An alternative network is a local-area network, which can communicate information much faster than most wide-area networks. A local-area network (LAN) is a collection of computers, usually personal computers, that share hardware, software and data. In simple terms, LANs hook personal computers together through communications media so the computers can share resources. Personal computers attached to a LAN are often referred to as workstations. All the devices - personal computers and others hardware - attached to the LAN are called 'nodes' on the LAN. As the name implies, LANs cover short distances, usually one office or building.