We use the term “see” because, when you feed your document into a fax machine, it uses a built-in photo sensor to view the page as a series of tiny squares (maybe just a hundredth of an inch each), and then records each square as either black or white. The reason older fax machines often used a rotating drum for paper-feeding was so the machine could record a single line’s worth of these tiny squares at a time, then rotate to the next line.
Once the fax machine has recorded a page’s contents, it converts each of the squares into a sequence of audio tones, using different tones to signify that a square is either white or black. (Cool, huh?)
To send your fax, your fax machine (in most cases) actually uses the plain-old telephone network. When you dial your recipient’s fax number on the machine’s keypad, and the two machines connect, your machine starts sending those audio tones over phone lines.
This is what you’re hearing as your fax machine makes those horrible screeching and beeping noises. It’s screaming to your recipient’s fax machine, telling it what to print: “Black square! White square! Black! Black! White, white, white! Black, white, black!”
Technology has come a long way since the 1840s, when the first fax device was invented—and since the 1980s, when the analog fax machines we described above went into widespread use in business.
So you can keep faxing like it’s 1989, standing over your desktop fax machine, waiting for it to finish screaming, “White square! Black square!”