Why did the internet make that unique sound when starting up back in the 90s?
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So, back in that era, the common (only?) method of getting online was for two computers to literally talk to each other over the actual telephone. That’s what dial-up Internet is.
In days even earlier than the 90s, your computer would have a literal dock that you’d plug the physical telephone handset into, and the computer would actually dial a number and whisper data into the speaker, and listen for whispers back. By the 90s, this had been streamlined to the point where the computer could tap directly into the phone line, no speakers and microphones needed. But they still played the startup noises out loud anyway. Even if no one really understood what the sounds were for, everyone who used dial-up knew what they were supposed to sound like, so if you heard it sound different, you could tell there was some kind of problem.
What the sounds actually are are data being sent from the computer at your end to the computer at the other end. More specifically, your computer will be hooked up to a special device called a *modem*, which is short for *modulator/demodulator*. That’s fancy jargon for “converter that can turn computer data on wires into noises (modulator), and back again (demodulator)”. It’s a translator that lets the computer turn signals that would normally travel up something like an Ethernet cable today into noises that can make it through a phone call. On the other end of the line will be another modem, which will be hooked up to a computer at your Internet service provider. Your computer has to talk to that computer to get through to the Internet.
The silly noises they make when starting a dial-up phone call is what we call a *handshake*. Basically, just the same way when you dial a strange number and hear a voice at the other end, there’s a kind of protocol everyone does. Answerer says “Hello” to let the caller know the other person is there and ready to listen, caller also response “Hello” to acknowledge that the caller has heard, then the caller usually states who they are and why they are calling.
Modems will go through a similar process to determine who they’re speaking to, what “language” they should speak in (not every modem supports the same capabilities, so they need to agree on something they both “speak”), and what extra settings they need to tweak to be able to hear each other loud and clear. Once it’s all figured out, data can flow through the line, and your computer gets connected to the Internet.
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The actual conversation will go something like this:
> Caller: *dials number*
> Receiver: “Hello. List your capabilities.”
> Caller: “Hello. I can list my capabilities. Can we start speaking faster so I can list them?”
> Receiver: “Sure.”
At this point, the receiver will send some special beeps that disable echo suppression. Remember that telephone lines are built to carry people’s voices. And it’s weird if you’re able to hear an echo of yourself come from the other end, so there’s tech in the phone system that slices these echoes out. That tech can actually get in the way of our Internet connection, though. There’s a magic tone that a modem can beep at that will tell the telephone system to disable it.
The conversation continues:
> Caller: “Here’s my list of capabilities.”
> Receiver: “Cool, here’s my own list of capabilities.”
Here, the phones both make some really loud high-low beep-boop noises. These noises are designed to send echoes down the physical phone line so the modems can listen to those echos and learn what the line is like. They will adjust their speaking patterns accordingly to best deal with the situation.
> Caller: “Okay, great. I’ve found a way where we can both talk and understand each other. Does <settings> sound good to you?”
> Receiver: “Yeah, sure that sounds fine. Let’s start talking like that.”
The conversation then shifts to random scrambled data, and some more listening to echoes in the phone line so the modems can learn more about how each other sound. At this point the speaker that makes the noises audible to the user cut out. Shortly afterwards, the connection will be complete and Internet data will start flowing.
All of this is shown in [this spectrograph](https://hackaday.com/2013/01/31/how-a-dial-up-modem-handshake-works/) of a common dial-up handshake. You can hear the audio synced up to the diagram and explained in more detail [in this video](https://www.youtube.com/watch?v=xp47x1EabqI).
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