In the ’90s, you reached the internet by calling an ISP (internet service provider) over your phone line. AOL, is that you?

There’s a nostalgic (or maybe just vaguely familiar to some of us now) screech that you would hear when you made that call. Here’s a bit of random history about where it comes from.

Phone lines were built to carry voice, meaning audio tones, not digital data. So a modem (modulator-demodulator; yes, we have entered Star Trek) converted your computer’s 1s and 0s into sounds and sent them to a modem at the ISP, which then converted them back.

How were they able to do that? Consumers had a modem at home, which is a device next to your computer or a card inside it that controlled the tones played over your phone line. That modem and the ISP’s modem followed a standard for the frequencies (e.g., the pitches sent back and forth) and which of those pitches meant a 1 versus a 0. This is unbelievable.

The screech is a script. First, the two modems compare lists of the standards each one supports and pick the best one they share. Then they send each other test tones to see how clean the phone line is, and settle on the fastest speed it can handle.

Another very valid question you might ask is, “Why in the world would phone lines be used to connect to the internet?” Because the phone network was the only wire that nearly every home was already connected to. Imagine trying to connect a wire to every single home in your neighborhood, and how expensive and time-consuming that would be.

This method of connecting to the internet had very real limitations, one of which was that you could only have one connection at a time, and the phone line was tied up the whole time. If someone needed to use the phone, or your sibling wanted to get online, you had to hang up first (hence “Get off the internet, I need to use the phone!”).