OCR Computing A-Level Revision

Data Transmission (1.5.c)

A diagram showing serial data transfer

Types of Connection

There are two types of connection - serial and parallel.

A serial connection uses just one wire. Therefore, only one bit can be transmitted at a time. This makes it simple to set up and reliable, as a second bit is not sent until the first arrives. However, this also makes the transmission speed slow.

Obviously parallel transmission is faster, as the devices are connected by more than one wire, so more than one bit can be transmitted at once. Parallel devices are normally connected using 8 (or a multiple of 8) wires, as then a whole byte can be transmitted at once. However, parallel connections are less reliable, as the bits can get muddled up due to the fine tolerances in the transmission.

Simplex

Simplex data transfer - like a one-way street

Simplex transmission is where data can only travel in one direction, for example a radio broadcast, where the radio station sends music or talk to a radio, but radios cannot send anything back to the station. It can also be thought of as a one-way street.

Half-Duplex

Half-Duplex data transfer - like a two way street that is only wide enough for one car

Half-Duplex transmission is where data can travel in both directions, however it can only travel in one direction at a time, for example a walkie-talkie, where only one person can have their "talk" button pressed. It can also be thought of as a two way street which is only wide enough for one car.

"Full" Duplex

Duplex data transfer - like a road

"Full" Duplex is where data can travel in both directions at the same time, for example an internet connection, where data can be both uploaded and downloaded at the same time. It can also be thought of as a two way street that is wide enough for several cars to pass, travelling in both directions.