One basic distinction is between parallel and serial communications. Computers use binary data, 0s and 1s that make up the instructions and data that they process. Binary digits (bits) are grouped into larger aggregations, for instance 8 bits makes a byte, characters are represented (in Unicode) by 16 bits and integers are typically 32 bits. When binary data is moved around a computer they are typically moved along 32 parallel wires (some computers now use 64 bits). These 'wires' are very fine and are etched in silicon so they don't take up much room. When data are transmitted between computers or across the globe they are sent in serial fashion, one bit after another along a single wire. It is cheaper to use a single wire for telecommunications and very high speeds of data transmission can be reached. Parallel data communications used to be used for printer cables but this method is scarcely used at all now as serial data transfer has taken over. Firewire and USB (Universal Serial Bus) are fast, cheap and effective and they have replaced parallel communication.
The main network topologies are: bus; star; ring.
A bus network is a single wire with computers and other devices connected to it. The cable runs from the server and is terminated by a resistor. Data run in both directions along the wires. Collisions between data are common, which makes them slow.
A star is where a device such as a hub or switch is used as the centre of a network with cables radiating out to connected computers. Data run in both directions between servers and work stations. Single cables between hubs and work stations reduces collisions and makes them easier to manage.
A ring network is where the computers are joined together by a ring of cable that links them all together. Data moves around the cable in one direction.
LANs are typically found in offices and schools and increasingly, using Wifi, in homes and public spaces such as hotels, transport terminals, shopping areas and beaches. LANs are typically owned by the organisation where they are hosted e.g. home, school, company. They are geographically limited: local.
WANs are networks, like the internet, that use telecommunications to link distant places. The hardware beyond the LAN is owned by telecommunications companies and governments.
Schools. Businesses. Hospitals. Accountants. Banks. Transport systems e.g. ticket machines - Oyster card needs a sophisticated network of card readers.