If you are asking about how fast the electrons flow down the cable, then the drift velocity, the average speed at which electrons travel in a conductor when subjected to an electric field, is about 1mm per second. So pretty slow. But if it’s the speed at which information can be be transmitted down a conductor that is of interest then this is determined by the speed of the electromagnetic wave rippling through the electrons, and that propagates at close to the speed of light. The dimensions of the wire and electrical properties, like its inductance, affect the exact propagation speed, but usually it will be around 90 per cent of the speed of light – about 270,000 km/s.
So if you want to get some information from point A to point B then you will be limited by this. Nothing can travel faster than the speed of light, and this is a limiting factor in the design of some electronics, such as processors, where things are being shrunk smaller and smaller to make the distance between two points as small as possible in order to increase the speed at which things can be processed. Although developments using quantum mechanics may provide a way of getting round this.
The main thing that we are usually interested in when it comes to cables is how much data can be sent down it at the same time. And this is affected by how the data is being propagated and the length of the cable. The higher the frequency being used, the greater the attenuation, or loss, the occurs as you get further down the cable. One of the things that happens in all electrical mediums, including cables, is that noise is generated by random electrons bumping into each other, and at some point the signal will get so low that it is comparable to, or less than the noise level and you won’t be able to distinguish the two apart. So for very short cable runs the frequency can be high, but for longer runs it needs to be lower.
So some guidelines are required so that you know which cable to use for various situations. For digital data transmission the two types of cables that are most frequently used are twisted pair and coaxial. Twisted pair cables can be specified to carry 10 Mbps (Mega bits per second), 100 Mbps, and 1000 Mbps (or 1 Gigabit) over distances up to 100 metres (plus a 10 metre tail at each end). Coax cables can be specified to carry 10 Mbps or 100 Mbps over distances up to 500 metres. Some internet service providers are able to get up to 1000 Mbps or 1 Gbps, although this is uncommon. There are some specialised cables that are used in labs that run up to 10Gbps.
Both twisted pair and coax cables can be used for Ethernet connections; twisted pair often referred to as thin Ethernet and coax referred to as thick Ethernet. The thin Ethernet, often sourced as CAT5E or CAT6 cable, is what is generally used to connect computer equipment together these days, and you will probably have some connected to your PC which links it into the internet. Thick Ethernet is generally used for backbone cables in buildings.
The above relates to what is referred to as baseband communication, i.e. there is no modulation. If modulation is used, where the data is superimposed on top of a modulation frequency, then much greater capacities of data can be carried. And with special coding equipment at either end then this can be increased further still. You will be experiencing this every time you watch a program on the TV. In the UK there are 69 possible UHF channels (or there were until some of them were sold off for mobile phone use) and each one can carry up to about 20 digital television stations. And all this will be coming from your television aerial down to your TV, for the tuner to sort out and display the station that you have selected. Just think of how much data that is. This is possible because the picture is coded and compressed at the transmission end and then decoded at the TV end. So the humble coax cable running from your aerial to your TV is carrying vast quantities of information or data, even though you are only accessing a small part of it at any one time.
