What are the differences between these superficially similar network components?

Category 5 network cables terminate in RJ45 plugs and a standard network card has just one socket. Therefore, only two devices may be linked directly, and even that requires a specially wired crossover cable. Using standard straight-through cable, or with more than two devices on the network, links must be made through a central exchange.

The simplest type is known as a hub. Data sent from a PC arrives at the hub and is transmitted to all the other connected devices. One of them will recognise that the data is addressed to it while the others ignore the signal.

Network equipment has a maximum throughput, or bandwidth. If your local cable carries data flowing between other computers, you must share the capacity. Hubs allow cables to carry data unnecessarily. This reduces the available bandwidth, slowing the system at busy times. Switches solve this by only passing data down the arms that link the devices involved in a transaction. Only if data is addressed to an unknown address does the switch transmit on all ports.

If your network is lightly used, the benefit of a switch over a hub will only be apparent occasionally. And if there are only two computers, there will never be a difference because the key benefit of a switch never comes into play. A heavily used network with three or more machines should show improved performance at least some of the time: more computers, better performance.

The purpose of a router is to link different networks, for example networks in separate buildings, or your own LAN and the one belonging to your ISP. The net is joined together with routers and couldn't work without them. A distinctive feature of the router is that if it receives data not destined for the network it is connected to, it forwards it to another router closer to the destination. It knows which one by means of routing tables that are regularly updated.