Parallel transmission refers to a situation when binary data transfer occurs simultaneously, while serial transmission refers to one in which binary data transfer occurs one bit at a time. Parallel transmission is faster, but more complicated, because each bit travels along its own data path. Serial transmission is normally slower but simpler, because each bit shares a data path.
Parallel and serial transmission are two methods computers use to transfer digital data. Laptops and desktops, especially if they are older models, may have both parallel and serial ports.
Parallel transmission is usually faster and moves more data, since it transfers eight bits. However it is more expensive since each bit must have a separate path. This means that each bit must have its own wire inside the cable. A parallel cable therefore has eight wires. This type of cable is also prone to distortion and noise. Older printers and table-top scientific devices such as multimeters are examples of equipment that uses parallel ports to communicate.
Serial transmission moves data one bit at a time, and so the cables only need one pair of wires to transfer data. One wire receives data, and the other sends it. Serial transmission is therefore cheaper, and it is preferred over parallel when there is a need to transfer data over long distances. On older computers, external modems are examples of devices that use serial communications. Serial ports on computers are also called COM ports. Serial transmission is normally slower than parallel transmission. However, some newer serial transmission circuits are able to match or even excel parallel transmission’s data transfer speed.