A computer network is made of computers which are linked to one another with communication lines (network cables, etc.) and hardware elements (network adapters, as well as other equipment for ensuring that data travels correctly). The physical arrangement -- that is, the spatial configuration of the network -- is called the physical topology. The different kinds of topology are:
Bus topology is the simplest way a network can be organized. In bus topology, all computers are linked to the same transmission line by using a cable, usually coaxial. The word "bus" refers to the physical line that joins all the machines on the network.
The advantages of this topology are that it is easy to implement and functions easily; on the other hand, it is highly vulnerable, since if one of the connections is defective, the whole network is affected.
In star topology, the network computers are linked to a piece of hardware called a hub. This is a box which contains a certain number of sockets into which cables coming out of the computers can be plugged. Its role is to ensure communications between those sockets.
Unlike networks built with bus topology, networks which use star topology are much less vulnerable, as one of the connections can easily be removed by disconnecting it from the hub, without paralysing the rest of the network. The critical point in this network is the hub, as without it, communication between the computers on the network is no longer possible.
In a ring-topology network, computers each take turns communicating, creating a loop of computers in which they each "have their turn to speak" one after another.
In reality, ring topology networks are not linked together in loops. They are actually linked to a distributor (called a MAU, Multistation Access Unit) which manages communication between the computers linked to it, by giving each of them time to "speak."
The two main logical topologies which use this physical topology are Token ring and FDDI.