Closeup of a serial port on a laptop.
Corbin Davenport / How-To Geek
Serial ports might be slow and not much use to most computer users these days, but thanks to their simplicity and reliability these ports may be with us for a long time yet.

While the parallel port is now safely buried in the grave of obsolescence, it may seem odd that the humble, slow serial port is still around. But as it turns out, bit-by-bit, this humble communications port has become essential.

What Is a Serial Port?

Not to get bogged down in semantics, but the “S” in USB stands for “Serial”, so technically a USB ports is a serial port. However, what we’re referring to here specifically is the 25-pin or 9-pin port that have been on PCs for many decades. Modern serial ports tend to be the 9-pin version, and the port’s shape and size is very similar to that of the (nearly obsolete) VGA port.

Regardless of how many pins a serial port has, it still transmits data one bit at a time in series. Hence the name “serial port.” The various pins on a serial port may have different functions, such as sending control signals or monitoring data from your connected device.

Serial ports are slow with the standard speed at the high end of the range coming in at a pedestrian 115.2Kbps. At that speed, it would take you almost a day to transfer 1GB of data! That’s under ideal circumstances, and things can be much, much slower than that.

Why We Still Use Them

If we have USB, and serial ports are so slow and comparatively bulky, why the heck do some computers still have them? There are a few reasons, but the most important ones include:

  • Lots, and lots, of industrial and scientific equipment are still in service and use serial ports to interface.
  • It’s simple, reliable, well understood, and much cheaper to implement than other more modern port types.
  • Hobbyists have uses, such as programming microcontrollers.

Serial ports can be easier to error-correct and many of the applications they are used for don’t need anywhere near the maximum standard bit-rate the port offers.

RELATED: Why Do We Still Use Analog Audio Ports?

We’re talking about simple binary control signals or plain text characters. Since the higher speeds of more complex interfaces would be wasted on these use cases, the reliability and simplicity of the serial ports become a much more valuable feature.

Motherboards With Serial Ports

While serial ports are still very much in use these days, mainstream computer users rarely, if ever, have a use for them. So you may in fact have a hard time finding any modern motherboards at all that include a 9-pin serial port as part of the I/O (Input/Output) ports on the back of the motherboard.

However, that doesn’t mean the motherboard doesn’t have a serial interface! Just like you probably have “headers” on the board to connect your PC case’s USB and audio ports to the motherboard, there’s a good chance there’s a serial port header on your motherboard. You’ll have to consult the motherboard’s manual to make sure this is the case, but if so you can simply buy an inexpensive header plate with a serial port and install it. It should be less than ten bucks! 16in (40cm) 9 Pin Serial Male to 10 Pin Motherboard Header Slot Plate

For motherboards with a compatible serial COM header, this is a cheap and easy way to add a serial port to your desktop PC

USB to Serial Adapters

If you’re using a laptop, don’t have a motherboard with the right headers, or don’t want to mess around inside your computer, another great solution is to use a USB-to-Serial Adapter. Just as the name implies, this converts USB signals to RS 232C serial port signals.

This will let you connect to any peripheral that uses a serial port, and allow you to interface with devices that accept serial port signals, using the right software of course!

Tripp Lite Keyspan High-Speed USB to Serial Adapter

Cheap, effective, compatible, and it needs no drivers or configuration in Windows. What more could you want?

Profile Photo for Sydney Butler Sydney Butler
Sydney Butler has over 20 years of experience as a freelance PC technician and system builder. He's worked for more than a decade in user education and spends his time explaining technology to professional, educational, and mainstream audiences. His interests include VR, PC, Mac, gaming, 3D printing, consumer electronics, the web, and privacy. He holds a Master of Arts degree in Research Psychology with a focus on Cyberpsychology in particular.
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