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The Difference Between Serial & Parallel Data Transfer

by G.S. Jackson

While the use of peripheral devices with Universal Serial Bus (USB) connections is ubiquitous at this point, there are still some devices, such as older printers, that use older connections such as parallel cables. Parallel cables do offer overall fast transfer, but serial cables offer a simplicity of implementation and thus ease of use. Also, serial connections are cheaper and thus have become a de facto standard for many computer devices such as MP3 players, printers and external hard drives.

Transmission Basics

When peripherals are attached to a computer, they require a physical cord to send signals back and forth. This way, the processor can communicate with these devices and send data to them. Communication occurs when the computer sends electronic pulses to the peripheral or vice-versa. These pulses aggregate into a message, a data file or a command. The alternating pulses are organized based on the type of peripheral device and how it interacts with the computer system.

Parallel Transmission

Parallel transmission occurs across a parallel wire. Parallel wires are flat and think, constituting multiple, smaller cables. Each cable can carry a single bit of information (either representing a 1 or 0). A parallel cable can carry multiple bits at the same time, one for each cable. An eight-cable parallel wire, for example, could carry an entire byte of data. This results in faster data transmission per second, all things being equal.

Serial Transmission

Serial transmission occurs over a single cable, one bit at a time. This type of communication is named "serial" not simply because data travels one bit at a time, but also because these bits must be organized in a particular way so that transmissions can be organized and considered trustworthy. For example, a single transmission from a peripheral device using serial data might take only 6 bits, so the serial mechanism has a way to dictate how to signal things like an "end of transmission."

Advantages and DIsadvantages

Parallel connections are, all things being equal, faster due to a higher rate of transfer. However, parallel ports also require more hardware, making them more expensive to implement. Furthermore, data transfer rates have increased to such an extent that serial connections can transfer entire gigabytes per second. Serial connections are also easier to implement, making them the go-to hardware choice for plug-and-play peripheral devices such as external hard drives and MP3 players.

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