The sound of getting online

For people who used dial-up modems, a certain burst of sound still triggers instant recognition. There was the telephone dial tone, then the ringing, a high-pitched answer, changing whistles, shushing noise and finally the blessed silence that meant the connection had settled.

It can be tempting to describe the handshake as computers simply saying hello. In reality, it was a negotiation between two devices trying to discover how to exchange information reliably across a telephone channel built primarily for voices.

The stages of the familiar noise

First, the calling modem dialed. If another modem answered, the devices exchanged signals indicating compatible standards and possible speeds. Different generations of modem used different training sequences and signaling methods. Depending on the equipment, the sounds could include sustained tones, chirps and broadband-sounding noise while the devices evaluated the line and established an operating mode.

Once they established the connection, they continued encoding computer data as signals suitable for the phone connection. Many modems muted their local speakers after connecting, so the call seemed to fall silent even though data was still flowing.

What did the speed mean?

A terminal might report CONNECT 2400, CONNECT 14400 or CONNECT 28800. Those result codes generally referred to negotiated connection rates, not the exact speed at which a file would reach your disk. Protocol overhead, compression, error correction, line quality and the remote system's speed all affected practical throughput.

Modem standards improved across the decades: 300 and 1200 bit-per-second connections gave way to 2400, 9600, 14,400, 28,800 and later 33.6k or nominal 56k download technology. Not every household phone line supported the highest advertised rate, and an old BBS might have a more limited modem than yours.

Carrier, retraining and disconnection

A carrier was the modem signal whose presence indicated that a data connection existed. If the modem lost that signal, many command-line interfaces displayed NO CARRIER. Line interference, a handset being picked up, a dropped telephone call or remote disconnection could all be possible causes.

When line conditions deteriorated, some modems attempted to retrain or fall back to a slower connection. Watching a transfer stall or hearing modem audio unexpectedly reappear could be nerve-racking, especially when a large ZIP download was almost finished.

Why the sound became an icon

Today's network connections are largely invisible. The dial-up handshake was audible evidence that a machine in one room had found another machine somewhere else. Because every BBS call began with that possibility of failure or success, the sound became part of the emotional memory of getting online.