In digital communications systems, there are 2 methods for data transfer: parallel and serial. Parallel communication uses multiple wires running parallel to each other, and can transmit data on all the wires simultaneously. Serial communication on the other hand, uses a single wire to transfer the data bits one at a time.

What is the History of Data Communication Networks?

Years ago, all data sent to and from disks traveled in serial form—one bit was sent right after another, using just a single channel or wire. With advancement in IC technology, it became feasible and cheap to put multiple devices on a single piece of silicon, and the parallel interface was born. The decreasing cost of integrated circuits, combined with greater consumer demand for speed and cable length, has led to parallel communication links becoming deprecated in favor of serial links. Typically, it used eight channels for transmission, allowing eight bits (one byte) to be sent simultaneously, which was faster than straight serial connections. The standard parallel interface used a bulky and expensive 36-wire cable.

Serial Vs Parallel Data transfer Interface

Data Transfer Speed

Speed of the parallel data transfer is extremely high compared to serial data transfer. An 8-bit parallel data transfer is 8-times faster than serial data transfer. In practice, clock skew reduces the speed of every link to the slowest of all of the links.

Complexity and Cost of Serial and Parallel Interface

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 to copy data onto a 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.

But in terms of transmission channel costs such as data bus cable length, data bus buffers, interface connectors, area occupied on printed circuit board (PCB), the parallel data communication is somewhat costlier.

Data Transfer Quality & Crosstalk Noise Interference

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. Crosstalk interference is more in parallel data interface, and hence the parallel data transfer is limited to shorter lengths only.

parallel ports suffer extremely from inter-symbol interference (ISI) and noise, and therefore the data can be corrupted over long distances. Also, because the wires in a parallel system have small amounts of capacitance and mutual inductance, the bandwidth of parallel wires is much lower then the bandwidth of serial wires. We all know by now that an increased bandwidth leads to a better bit rate. We also know that less noise in the channel means we can successfully transmit data reliably with a lower Signal-to-Noise Ratio, SNR.

High Frequency Performance

In the competitive consumer electronics technology, the speeds of data transfer are increasing day by day. But unfortunately parallel buses are hard to run at high frequencies for a number of reasons the greatest of which are:
1. It is hard to route many signals across a board without introducing timing variation (clock skew) between them – the more variation the lower maximum frequency is.
2. Many wires switching simultaneously produce lots of EMI and interfere with each other. More EMI leads to less maximum frequency.

Flexibility to Upgrade the Data Communication Software/Hardware

Serial interface is more flexible to upgrade as it has lesser hardware, and the upgrade to the higher versions is possible at software level without changing the hardware, whereas the parallel data transfer mechanism more rely on hardware resources and hence difficult and costlier.

For example, recently PCI Express(serial) is introduced and another standard PCI X(high speed parallel), but you would have heard about PCI Express only because it is compact use the same type of connector with huge bandwidth the main thing is that it is serial, now the serial bus standards are overtaking parallel ones because of their high speed flexibility as you can easily change the internal protocol not useful or possible in parallel transfer, and design and production cost.

What is the latest Trend? Serial or Parallel

Now the latest trend is the usage serial data communication for desktop PCs, portable devices, vehicle interface networks, storage media interface, peripheral data transfer, etc. Most of the latest printers don’t even come with parallel ports anymore. Laptops have dropped traditional parallel and serial ports in favor of higher-speed Universal Serial Bus and IEEE 1394 ports.

We’ve already seen serial interfaces displace parallel ones for printers and other peripherals. Now, inside computers, equipment manufacturers are replacing parallel connections to disk drives and arrays, both SCSI and Advanced Technology Attachment (ATA), with a new serial architecture called Serial Attached SCSI and Serial ATA.

How to Choose the Best Data Transfer Interface from Serial or Parallel?

Parallel- short distance.
Serial – longer distance.
Parallel- Low speed/frequency data transfer.
Serial – High speed/frequency data transfer.

Nowadays, clock frequency is a most important thing to determine the performance of a system. Due to the EMI reasons and the cross noise between wires, the SERIAL is better than the PARALLEL.