What is the difference between Serial and Parallel Communication?

Think of the communication stream like a single laned road (serial) and a highway (parallel). Although the data is going in one direction, the data is sent bit-by-bit with serial communication (single lane road-car by car). With parallel the data is moved multi bits at a time (a multi lane highway going in the same direction with full of traffic) feature: serial communication means less number of wire and it is slow, one by one bit of message signal is send to receiver.parallel communication has so many numbers of wire & it is fast.

Serial communication : Modem.

Parallel Communication : Printer.

Serial Communications and Parallel communications both define a way of transportation of data over networks.

  • In Serial devices: transmit data bit-after-bit, serially over time. When 8 bits are received, after 8 bit-times (plus a little extra for signal synchronization), they are assembled back into a byte and delivered to the software. A serial link transmits a single stream of data.
  • In Parallel communication: a word of some data length, say like 8 bits, travels all at once, along multiple parallel channels (one channel per bit position). At the receiver, an 8-bit byte is received every "bit time". In effect, you have 8 serial channels transmitting and receiving data simultaneously, making it (by definition) at least 8 times faster than a single serial channel using the same transceiver technology.

From a system perspective, you can also refer to "parallel" channels for redundancy of critical serial streams, where multiple identical copies of data are sent simultaneously, and the receiver decides which data is valid, often by "voting" after detecting errors in the data on one or more channels. In this case, the parallel channels provide no increase in data throughput (compared to a single error-free channel), other than by reducing the need for time-consuming re-transmissions when errors are detected. It is a trade-off between speed and reliability. A parallel link transmits several streams of data (perhaps representing particular bits of a stream of bytes) along multiple channels (wires, printed circuit tracks, optical fibres.

Both serial ports and parallel ports are examples of computer technology that were once cutting edge, but now have been replaced by newer methods of transferring data from hard drives to ancillary devices. However, there are many personal computers and other devices in use today that make use of a serial port, a parallel port, or both. The difference between the serial and parallel port is not always understood, owing to the similar design of both ports. Here is some background on each type of port and what they were designed to accomplish.

Of the two, the parallel port is the older port design. The first use of a parallel port was in the early 1970's and allowed printers to be hooked directly into a mainframe and print orders carried out by entering a section of code through the command station. The parallel port allowed for a one way transmission of data from the source to the printer.

As the personal computer came into common use, the parallel port remained a popular option for attaching a printer to the hard drive of the system. In some circles, the port became commonly known as the printer port, since that function was the most common application of the device. Some manufacturers would go as far as customizing the design of the parallel port so that only certain types of printers could be used with certain brands of personal computers. However, by the mid 1990's, the parallel ports on most personal computers had been standardized to accommodate just about any make and model of printer.

In addition, the parallel printer became somewhat more functional, in that the design was used to provide one way communication between the hard drive and a number of ancillary devices. Early external modems and storage devices are a couple examples of the broader use of parallel ports. However, since the beginning of the 21st century, the parallel port has largely been replaced by the USB port, although some ancillary devices still allow for connection by both means.

One key difference between a serial and parallel port is that the serial port allows for data to be transferred in from a remote device or transferred out from the hard drive to a remote device. This two-way communication process makes it possible to connect workstations to larger terminals as well as a wide range of peripheral devices.

For most of the history of personal computers, both the serial and parallel port were the most common means of data transfer and communication. However, with both the serial and parallel port replaced by the use of USB ports, fewer new devices are designed to include either a serial or parallel port. Older personal computers that feature a serial and parallel port often require an adapter cable in order to make use of the latest generation of peripheral devices.

A Shift of Course

Here is an example of how the PC is moving "away'" from parallel to serial interfaces. Early generations have been apart of the parallel design that allows multiple bits sent simultaneously over several pins in parallel. The faster the bits are sent the better, but the timing of signals must be the same. This becomes more difficult with faster and longer connections.

A serial bus design is much simpler, sending 1 bit at a time over a single wire at much higher rates than parallel. By combining multiple serial data paths, even faster speeds can be realized that dramatically exceed the capabilities of traditional parallel buses.