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What is the Difference Between a Serial and Parallel Port?

Malcolm Tatum
Updated May 16, 2024
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Both serial ports and parallel ports are examples of computer technology that were once cutting edge; for most of the history of personal computers, both the serial and parallel port were the most common means of data transfer and communication. With technological advances, both the serial and parallel port have largely been replaced by the use of USB ports, and fewer new devices are designed to include either a serial or parallel port.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. Perhaps the main difference between a serial and parallel port is the way information is communicated: a parallel port is only able to transfer information from the hard drive, while a serial port can transfer information both to and from a hard drive.

Parallel Ports

Of the two, the parallel port is the older port design with the first use in the early 1970s, allowing 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 allows for a one-way transmission of data from the source to a secondary device, such as a printer. In some circles, the parallel port became commonly known as the printer port, since that function was originally the most common application of the device. Early external modems and storage devices are a couple examples of the broader use of parallel ports. Since the beginning of the 21st century, the parallel port has largely been replaced by the USB port, although some ancillary devices still allow for connection by both means.

Parallel ports generally have a minimum of 25 pin connectors that make up the actual connecting part of the device. These 25 pins will match up with the end of the device that the port is being connected to and it is through the pins that information is transferred. Each pin connector performs a different function.

Serial Ports

One key difference between a serial and parallel port is that the serial port allows for data to be transferred to the hard drive from a remote device or transferred from the hard drive to a remote device, as opposed to the parallel port's outbound-only communication; a serial port can also be referred to as a communication port or bi-directional port. This two-way communication process makes it possible to connect work stations to larger terminals as well as a wide range of peripheral devices such as external hard drives or smart phones. Serial ports are known to be slower than parallel ports, however, because they can transfer information in two directions simultaneously.

A serial port will usually be made up of either nine or 25 pin connectors; several of the connectors in a 25 pin port are not used regularly. Originally, a nine pin port was believed to be more compact and cost-effective, but often it was not efficient enough to serve its purpose.

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Malcolm Tatum
By Malcolm Tatum
Malcolm Tatum, a former teleconferencing industry professional, followed his passion for trivia, research, and writing to become a full-time freelance writer. He has contributed articles to a variety of print and online publications, including EasyTechJunkie, and his work has also been featured in poetry collections, devotional anthologies, and newspapers. When not writing, Malcolm enjoys collecting vinyl records, following minor league baseball, and cycling.
Discussion Comments
By dkarnowski — On Nov 04, 2010

@summertime, I actually ran into a very similar issue with specialized bar scanners that our computers and point of sale systems were using. These scanners simply were to expensive to replace and when we purchased new computers to hook up to them, we realized that no parallel port was included on the new system. At first, I gawked in disbelief. How could such a true and tried system of connection be phased out within a generation of computers. Trying to avoid the high cost that you speak of to transition to new equipment, we found an option that seemed to work best and was quite cheap.

We found that some computer hardware manufacturers learned that consumers still had a need for these older technologies and. The best option for our needs and the constraints of the new computers was the installation of a parallel pci card. This expansion style card that installs into the motherboard directly worked great and had a small cost. Working with drivers for the operating system was the most challenging part but luckily we did our research and found a card that was capable of working on Microsoft's latest version of Windows. I hope others are able to make a costly transition less painful with the use of expansion cards.

By summertime — On Nov 04, 2010

The only problem with the phasing out of the rs232 serial port from many home and professional level computer systems is that it will result in a large variety of perfectly working hardware becoming obsolete or unusable. A good example of this is the use of a scrolling LED marque that my business uses to display messages to customers. Traditionally we had programed this message board with a computer that was used specifically for that purpose. Last week when that computer ceased to continue working, we were faced with a major problem. The replacement computer and any computer that we researched did not come with this old style of serial port. While I did find some references to serial to usb converters available on the internet, the two that I ordered and tried simply would not work. I was then told by the manufacturer of the sign that it was not longer possible to update the sign via a computer and would have to be done with the very inefficient remote control.

This was unacceptable and the company offered me a trade in bargain on my ancient technology. Essentially I paid a very little amount to get a better message board and USB connectivity. This is always something to consider when you have to deal with equipment that uses archaic connection standards. Be careful as a business owner as this is the type of situation that can greatly increase costs as you make a transition.

By IceCarver — On Nov 04, 2010

I recently retired my very old ink jet printer and realized that the new printers that are on our market today have a new type of connectivity. While I was expecting the usual and time-tested parallel port print, that was far from what I experienced. It might also speak to just how old the computer I have is. My folks always raised me with the value that you don't replace something until it is beyond repair. Following this philosophy means that I have an ancient computer that has finally become more expensive to repair then purchase a new system.

So after needing a new computer and new printer, I quickly found that I had no idea what half of the new connectors on the back of the tower were for. Luckily computer manufacteres have caught on to the fact that consumers have a much easier time with color codded connectors. My biggest surprise was the use of USB for my new keyboard, mouse and printer. The mouse and keyboard were no brainers but the problem of how to hook up my printer remained. The new printer didn't come with a cable and with that realization, it occurred to me that things haven't changed that much. You still have to pay extra for a cable, no matter the connection type, it's just marketing.

By spreadsheet — On Nov 04, 2010

I am so glad that the use of parallel and serial ports have been phased out of the current computer hardware market. Gone are the days of dealing with gender adapters and making sure that you had a very specific cable for a specific application. Also gone are the days of ridiculously slow connection and data transfer rates that could drive a poor computer tech or user insane.

With the advent and the mass introduction to the market of the Universal Serial Bus, we have overcome all the old issues that came along with using a serial port. I just hope that while USB is great for now, that one day it is replaced with faster and more universal standard for accessory connectivity. For most things the current USB 2.0 standard works well for but I can see where certain things can use a faster transfer rate.

A good example of this is the use of external hard drive storage for the editing of video. My personal computer does not have enough internal space to deal with the massive file sizes that come along with video. The problem with using external storage is the computer is constantly battling a slow transfer speed that can't keep up with the modern day processors and editing applications.

Malcolm Tatum
Malcolm Tatum
Malcolm Tatum, a former teleconferencing industry professional, followed his passion for trivia, research, and writing...
Learn more
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