A fax machine scans a document into pixels, converts those pixels into audio tones, and sends them over a telephone line — where a second machine reassembles and prints them. Here's exactly how it works, what's inside the machine, and why millions still use fax today.
Frequently Asked Questions
How does a fax machine work step by step?
A fax machine scans your document into a grid of black-and-white pixels, compresses the data, converts it into audio tones, and sends those tones over a telephone line. The receiving machine decodes the tones back into pixels and prints the page. The entire process typically takes 30 seconds to 2 minutes per page.
What are the main components of a fax machine?
A fax machine contains three core systems: a scanner (reads the document), a modem (converts data into phone-line tones and back), and a printer (reproduces the received document). It also includes a telephone handset connection, a document feeder, and control electronics.
Why does a fax machine make a screeching sound?
The screeching noise is the T.30 handshake — the two fax machines exchanging tones to negotiate transmission speed, resolution, and error-correction settings before any document data is sent. It lasts 3–5 seconds and is a normal part of every fax call.
What is the difference between a thermal fax and a plain-paper fax?
Thermal fax machines print on special heat-sensitive paper that fades over time and cannot be highlighted. Plain-paper fax machines (laser or inkjet) print on regular paper, producing durable, permanent copies. Most modern offices use plain-paper multifunction printers that include fax functionality.
Do I need a fax machine to send a fax today?
No. Online fax services like mFax let you send and receive faxes from your phone or computer — no machine, phone line, or paper required. You upload a document, enter a fax number, and the service transmits it over the same phone infrastructure as a physical machine. The recipient cannot tell the difference.