Facsimile Machine

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What Does Facsimile Machine Mean?

A facsimile (fax) machine uses public switched telephone networks (PSTN) and the Internet for the electronic fax transmission of text and images.


Digital fax machines use modified Huffman and modified read data compression formats and scan 100-400 lines per inch (LPI).

Fax functionality is segmented by class, group, data transfer rate (DTR) and conformance with the International Telecommunication Union’s Standardization Sector (ITU-T).

Fax machines are also known as telefax machines, telecopy machines or telecopiers.

Techopedia Explains Facsimile Machine

In 1843, Alexander Bain introduced fax technology in the form of a two-pen and two-pendulum apparatus that reproduced handwriting via an electrically conductive surface. More recent fax technology advancements have facilitated a shift from traditional fax machines to server and cloud options. For example, direct fax routing, such as email, lowers costs by eliminating unnecessary hardware like landlines and printers. Fax machines continue to evolve to meet market demands for convenient communication methods.

Fax machines are grouped as follows:

  • Groups 1 and 2: Scanned lines are transmitted as continuous analog signals. Horizontal resolution depends on scanner, printer and transmission quality. Group 1 conforms to ITU-T Recommendation T.2 with approximate transmission of six minutes per page and 96 LPI vertical resolution. Group 2 conforms to ITU-T Recommendations T.30/T.3, with approximate transmission of three minutes per page and a 96 LPI vertical resolution. It is also interoperable with Group 3 machines.
  • Groups 3 and 4: Digital compression is used to reduce transmission time. Group 3 conforms to ITU-T Recommendations T.30/T.4 with approximate transmission time of six to 15 seconds per page and fixed horizontal and vertical resolutions, as per T.4. Group 4 conforms to ITU-T Recommendations T.563/T.503/T.6/T.62/T.70/T.72/T.411-T.417, operates at 64 Kbps as per digital Integrated Services Digital Network (ISDN) circuit with a T.6 resolution and T.4 superset.

Fax machine modem classes are designated according to CPU requirements as follows:

  • Class 1: Transmission time is six minutes or less. Connects to a PC and sends data as block frames only. No frame multitasking. Aborts during busy signals. The slowest versions transmit analog data.
  • Class 2: Transmission time is two minutes or less. Connects to a PC or other enabled device. Organizes data by software session receiving modem transfer commands. No frame transmission. Handles multitasking.
  • Classes 3 and 4: Transmission time is 10 seconds or less. Most versions work without a computer or software. Ideal for multitasking and email. Less expensive than Class 2. No bulky equipment required.

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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.