Why did the internet make that unique sound when starting up back in the 90s?
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That is the sound made by a modem (modulator/demodulator), which communicates with another computer over the phone. Modems had speakers which played the first few seconds of their output and what they were hearing back over the phone, so the user could be sure their hardware was communicating correctly.
You are probably talking about dial up modem, that was used to connect to internet trough phone network back in the day.
Why? Dialing up was done by sounds… Just like regular calls… That’s why pressing numbers on landline makes different tones… And so does smartphone… As inherited feature
That sound was your modem talking to the modem on the other end of the phone line. They basically start slow and then speak faster and faster and faster and faster until the other modem is like “wait, I lost you.” And now they know how fast they can talk to each other.
Pretty sure it was only audible to humans because the handshakes took a while and people are really impatient when it seems like nothing is happening. Less an engineering constraint and more a marketing one.
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).
Dialup internet used ordinary phone lines, so its communication had to be done with sounds. When you’d first set up a connection, the modem would play the sounds out loud as well as through the phone line to help you diagnose if there was any issue with the connection.
The sounds that it would play out loud were a “handshake” with your internet service provider’s modem. Basically the two modems were talking to each other to figure out how to set up the connection.
Originally computers connected to each other over normal telephone lines.
You have old-fashioned landline telephones, like you may have seen in old movies or movies set in the past, that had handsets that looked like the symbol for telephone: 📞
You could put that handset on a device connected to a computer that was basically just a microphone and a speaker.
The computer would make sound into the part that humans would speak normally and listen for sound from the part that humans would put their ear on.
On the other end of the telephone call another computer would do the same.
[It would look something like this picture from wikipedia](https://upload.wikimedia.org/wikipedia/commons/thumb/c/cc/Coupleur-accoustique-IMG_0298.JPG/320px-Coupleur-accoustique-IMG_0298.JPG).
Computer would literally use this to talk with each other via a series of beeps.
Before they got to that point they first had to make sure they were on the same page. The computers slowly had figure out that they were both talking the same way and could both talk and listen at the same speed. They would start slowly and than explain to each other what type of functions they both supported and needed and what max speed they could both handle.
These beeps and bits were much slower than normal “talking” because they had to be make the negotiation of what they were both capable of at the lowest possible level.
Eventually someone figured out that since the signals in the telephone line were electrical and the computes were electrical it made little sense to transform the signals into sounds and then have a telephone-receiver transform those sounds back into electrical signals.
You could just create a device that you could plug directly into a telephone jack, like a landline telephone or fax machine or answering machine and have that connect to the computer.
There was no need for actual noises to be made, you could just send the signals those noises were supposed to create in a microphone directly through the wire.
However people who had been using the older style modems that did make noises, had found the noises sometimes useful.
If you knew what was happening you could listen to the computer negotiating with the other side and establishing a connection.
More importantly you could listen to where something went wrong.
People could tell when the sound of the connection being established didn’t sound the way it was supposed to and even understand which part had gone wrong.
It was a very nerdy skill to have, but in those days mostly just nerds used those things.
So modems got a speaker through which they could play the whole back and forth of the connection being established for diagnostic purposes.
People could hear the number being dialed, the other side picking up the back and forth as they negotiate each others capabilities and tested the quality of the phone line they were talking over and then did a quick test of things like equalizer and echo canceling at the end and then the speaker would cut out and the computers would talk to each other without that being transformed into noise.
Obviously this was not useful info for everyone and there was a command that you could send to your modem to tell it to stop actually putting that part though to the speaker.
However you needed to either have read your manual carefully or had someone on a bulletin board or a the USENET explain it to you or come across it in a computer magazine in order to know that command.
Many people never figured that part out or were to lazy to do it or like the sound it made and thus this optional diagnostic feature was stuck on for many computer users.
People even if they could not make use of it came to expect it.
Later when stuff like winmodems and softmodems came out they didn’t actually have the ability to make that sound anymore, but people still expected the sound so much that the would simply play an audio file of a generic dial-up connection sound. It was useless for any sort of diagnostic purposes since it was just a recording not the live sound of the connection being established, but it gave people the reassuring sound they expected at that point.
So it came from a feature that original had real use to something useless that was kept on because people expected to hear it.
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