Soon after the first IBM PCs hit the market in the 1980s and rapidly became accepted as a business tool, the advantages of connecting these small computers became obvious. Rather than supplying every computer with its own printer, a network of computers could share a single printer. When one user needed to give a file to another user, a network eliminated the need to swap floppy disks. The problem, however, was that connecting a dozen
computers in an office with individual point-to-point links between all of them was not practical. The eventual solution to this problem was the local area network (LAN).
A LAN is a group of computers connected by a shared medium, usually a cable. By sharing a single cable, each computer requires only one connection and can conceivably communicate with any other computer on the network. A LAN is limited to a local area by the electrical properties of the cables used to construct them and by the relatively small number of computers that can share a single network medium. LANs are generally restricted to operation within a single building or, at most, a campus of adjacent buildings.
Some technologies, such as fiber optics, have extended the range of LANs to several kilometers, but it isn’t possible to use a LAN to connect computers in distant cities, for example. That is the province of the wide area network (WAN) .
In most cases, a LAN is a baseband, packet-switching network. An understanding of the terms baseband and packet switching, which are examined in the following sections, is necessary to understand how data networks operate because these terms define how computers transmit data over the network medium.