Data transmission
Serial data transmission
If a piece of data is stored as an 8 bit binary code such as 10111010, and you have only one wire, you can still send this data down the wire. You do it by sending the code one bit at a time. This is known as serial data transmission.
Parallel data transmission
If a piece of data is stored as an 8 bit binary code such as 10111010, and you have 8 wires, you can send this data by sending the data bits down the 8 wires, 1 bit for each wire. This is known as parallel data transmission. Parallel data transmission is clearly a lot faster than serial transmission, but you need more wires. There is also a problem when distances over about 10 meters are involved. If you are sending lots of 8 bit codes, they start to get out of syncronisation with each other and that leads to lots of data transmission errors. This is why parallel data transmission is reserved for connecting devices that use a high volume of data but are close to the computer, like printers and scanners, for example.
Data transmission definitions
When data is moved from one place to another, we talk about 'data transmission'. You can classify data transmission into different categories known as simplex, half-duplex and duplex. These terms are described below.
Simplex data transmission
When data transmission can only take place in one direction, we talk about 'simplex transmission'. Teletext is a classic example of simplex transmission. Data is broadcast by television companies at the same time as TV pictures and picked up via aerials in people's homes. People do not send back signals from their television to the aerials. Of course, you can use a handset to send requests for pages to your TV's special Teletext adapter and the special Teletext adapter then captures the requested Teletext pages when they get broadcast. The requests don't get sent from the TV back to the transmitters.
Half duplex transmission
Simplex data transmission is one-way communication. 'Half duplex communication' is the term given to communication that can happen in both directions but not at the same time. The classic example of this is a set of walkie-talkies. Each handset can be used to either send or receive but cannot do both at the same time.
Duplex data transmission
Duplex data transmission is the term used to describe any communication that takes place in both directions at the same time. The classic example of this is the telephone. You can both send and receive information at the same time. You can both talk and hear at once!