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What is "serial data"? What is "parallel data"?

If you've ever looked at the inside of a computer at a circuit board, such as a motherboard or a video adapter card, you've seen the scores of gold wires running over the board parallel to one another. These wires, called the bus, are how data is transferred from one part of the computer to another. (If you've never seen this, you really should sometime soon.) Computers think and work in "binary": 1's and 0's, true or false, on or off. In order to work more efficiently, a computer "word" (a particular series of 1's and 0's) is transmitted at once on parallel wires. A 1 is generally transmitted by applying a +5V (high) voltage to a given wire, and a 0 by applying a +0.5V (low) voltage. To transmit a word like 10010110 (an 8-bit data word), you need 8 parallel wires on the bus. First, the computer applies a 1 to the first wire, a 0 to the second and third wires, a 1 to the forth, and so on. This is how parallel data streams flow in a computer.

There are often cases when a computer needs to communicate signals to other devices or other computers, and will not necessarily have all the wires needed to do so. The data can be transferred on a single wire if the bits can be lined up and sent in order, and you have a way to tell when one word stops and the next one starts. This is the "serial data" format, in which data is sent in series. It is what makes it possible to transmit data over the phone lines and out into the cloud of computers we call the Internet.


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