How a Fax Machine Works – From Start to Finish

Last Update: August 9th, 2021

This page is about a how a fax machine “works” (the technology behind it).

For how to use (and set up) a fax machine (the actual operation of it) see our page on “how to set up a fax machine.”

The ability to send an image over a wire predates Alexander Graham Bell’s invention of the telephone. Today’s fax machines work with many of the same concepts as those earlier devices, but with today’s technology.

Table of Contents

How faxes communicate

All fax machines and fax transmissions revolve around the same basic concept – they scan a document, transfer the image of that document over to a signal, then send that signal to another fax machine that decodes the signal and prints the document back out.

How Fax Machines Work

Early fax machines worked on two tones – one for there being an image on a certain point on the page, and one for not being an image on a certain point on a page. This system would result in either a black dot or white dot being transmitted over to the other machine.

Just like a computer screen or LCD display is made up of many tiny dots to put a picture together, a fax records that information to send it back in much the same way.

Today’s fax machines are much close to a scanner hardwired into a printer then they are the models from 10-20 years ago. Digital technology has made for a much more accurate picture as well as faster and compressible transmissions.

A Fax Transmission Example

A fax transmission works in steps – the fax machines handshake, transmit their message, and the send confirmation.

Step 1 – the Handshake

The handshake is the first part of a fax communication.

The sending machine waits for the line to pick up and then starts sending a series of beeps.

These beeps signify that the machine is requesting to send a fax. The sending fax machine is essentially saying “Hey! I’m a fax machine! I’m looking for another fax machine! Is there one there?”

If the machine on the other end is also a fax, that fax will answer the beep with its signal. At this point, the receiving fax machine is saying “Hey you’re a fax? Guess What? I’m a fax too!” And both machines now know that they’ve each made a friend.

Once both machines have acknowledged each other, they send information back and forth about them (just like two people getting to know each other). This information is along the lines of whether they are analog or digital faxes, as well as what compression formats they speak.

Once the two fax machines understand what the other is capable of, they decide on a format to send with and then start their transmission.

Step 2 – Transmission of Messages

After the handshake has occurred, the sending fax will send the message through to the receiving fax.

As both machines know that they speak the same language, they’re able to send the messages through in a format that they know the other machine knows.

Step 3 – Confirmation of Message Reception

The final step is the confirmation of the message being received. The receiving fax machine will send a confirmation notice, which the sending fax machine can now print out.

Today’s fax technology

Today’s version of fax has changed very much from the power machines of the 1980s and 90s.

The majority of fax transmissions now happen through online fax services, fax servers, or fax boards that are part of larger multifunction machines.

Most of today’s fax machines consist of three parts:

  • A scanner
  • A printer
  • A fax modem (phone line)

When sending a fax, the scanner and fax modem work together – the scanner by capturing the document and turning it into a digital signal, and the fax modem by sending that signal over the phone line.

When receiving a fax, the printer and the fax modem work together – the fax modem by collecting the digital signal that arrives over the phone line, and the printer by turning that digital information into a printed piece of paper.

The benefit of this approach is that fax technology can work with some printing technologies (ink and toner, across different brands), or a combination of machines (scanning in one area, printing in another, and transmitting faxes through either machine or a computer’s fax server).

Fax options on a multifunction unit (printer / scanner / copier / fax)

When a fax machine is part of a unit that also prints, scans, and copies, it is called a “multifunction product” “multifunction printer” or “MFP.”

When a fax is present on an MFP, the fax modem in the fax part of the machine works with the scanner and the printer portion of the MFP to scan or print the fax.

Fax Servers and Online Fax Services

The largest shift in fax technology has come from a shift towards fax servers and online fax services.

An online fax service is a system that provides users the ability to fax without having a fax machine or a phone line. A fax service is accessed through the internet and takes care of the technical details while the user has access to an interface that is very much like web-based email programs such as Hotmail or Gmail. Online fax services also have features such as being able to send and receive faxes through email.

A fax server is very much like an online fax service. However, it is typically used in an enterprise level system (run by an organization’s IT department) with many users sharing the resource.

The fax machine of the late 20th Century

Fax machines hit their peak in the decades of the 1980s and 1990s.

A fixture in every office, home use of the fax machine was also widespread.

Late 20th-century fax machines pre-dated the multifunction unit – they were standalone devices and worked on technology closer to that of traditional photocopiers than of today’s printers.

Pre 1960s Fax Machines – the History of Fax

Before the introduction of the “modern” fax machine around the mid-1960s, fax was in place in different formats for almost a century.

A service with the ability to electronically transmit an image over distance was in place in France at the time that the US Civil War was ending (at the time Alexander Graham Bell, the inventor of the telephone, would not even have been 20).

The first systems existed as a connection between two synchronized clocks, and later using pieces of chemically impregnated paper. The first true example of a fax transmission used Telegraph lines were used in the first true example of a fax transmission.

Between the 1860s and 1960s, facsimile transmissions went through some changes but remained an important part of communications in business and government – from sending maps during wartime to other functions where courier would be too slow.

For more on fax machines in the Pre-1960s era, see our page on “The History of Fax.”

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