Editing Parallel communication (section)

==Comparison with serial links==
Before the development of high-speed serial technologies, the choice of parallel links over serial links was driven by these factors:

* Speed: Superficially, the speed of a parallel data link is equal to the number of bits sent at one time times the [[bit rate]] of each individual path;  doubling the number of bits sent at once doubles the data rate.  In practice, [[clock skew]] reduces the speed of every link to the slowest of all of the links. However, parallel lines have lower latency than serial lines, this makes parallel lines is still used on memory bus like [[DDR SDRAM]].
* Cable length or link length: [[Crosstalk (electronics)|Crosstalk]] creates interference between the parallel lines, and the effect worsens with the length of the communication link.  This places an upper limit on the length of a parallel data connection that is usually shorter than a serial connection.
* Complexity: Parallel data links are easily implemented in hardware, making them a logical choice.  Creating a [[parallel port]] in a computer system is relatively simple, requiring only a [[Latch (electronic)|latch]] to copy data onto a [[Bus (computing)|data bus]].  In contrast, most serial communication must first be converted back into parallel form by a [[universal asynchronous receiver/transmitter]] (UART) before they may be directly connected to a data bus.

The decreasing cost and better performance of [[integrated circuits]] has led to serial links being used in favor of parallel links; for example, [[IEEE 1284]] printer ports vs. [[USB]], [[Parallel ATA]] vs. [[Serial ATA]], and [[FireWire]] or [[Thunderbolt (interface)|Thunderbolt]] are now the most common connectors for transferring data from [[audiovisual]] (AV) devices such as digital cameras or professional-grade scanners that used to require purchasing a SCSI HBA years ago.

One huge advantage of having fewer wires/pins in a serial cable is the significant reduction in the size, the complexity of the connectors, and the associated costs.  Designers of devices such as smartphones benefit from the development of connectors/ports that are small, durable, and still provide adequate performance.

On the other hand, there has been a resurgence of parallel data links in [[radio frequency|RF]] communication. Rather than transmitting one bit at a time (as in [[Morse code]] and [[BPSK]]), well-known techniques such as [[Phase-shift keying|PSM]], [[Pulse-amplitude modulation|PAM]], and [[Multiple-input multiple-output]] communication send a few bits in parallel. (Each such group of bits is called a "[[Symbol (data)|symbol]]"). Such techniques can be extended to send an entire byte at once ([[256-QAM]]).