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Apr 1, 2020

Today we’re going to look at the history of the dial-up computer modem. 

Modem stands for modulate/demodulate. That modulation is carying a property (like voice or computer bits) over a waveform.  Modems originally encoded voice data with frequency shift keys, but that was developed during World War II. The voices were encoded into digital tones. That system was called SIGSALY. But they called them vocoders at the time. 

They matured over the next 17 years. And then came the SAGE air defense system in 1958. Here, the modem was employed to connect bases, missile silos, and radars back to the central SAGE system. These were Bell 101 modems and ran at an amazing 110 baud. Bell Labs, as in AT&T.  

A baud is a unit of transmission that is equal to how many times a signal changes state per second. Each of those baud is equivalent to one bit per second. So that first modem was able to process data at 110 bits per second. This isn’t to say that baud is the same as bitrate. Early on it seemed to be but the algorithms sku the higher the numbers. 

So AT&T had developed the modem and after a few years they began to see commercial uses for it. So in 1962, they revved that 101 to become the Bell 103. Actually, 103A. This thing used newer technology and better encoding, so could run at 300 bits per second. Suddenly teletypes - or terminals, could connect to computers remotely. But ma’ Bell kept a tight leash on how they were used for those first few years. That, until 1968.

In 1968 came what is known as the Carterphone Decision. We owe a lot to the Carterfone. It bridged radio systems to telephone systems. And Ma Bell had been controlling what lives on their lines for a long time. The decision opened up what devices could be plugged into the phone system. And suddenly new innovations like fax machines and answering machines showed up in the world. 

And so in 1968, any device with an acoustic coupler could be hooked up to the phone system. And that Bell 103A would lead to others. By 1972, Stanford Research had spun out a device, Novation, and others. But the Vladic added full duplex and got speeds four times what the 103A worked at by employing duplexing and new frequencies. We were up to 1200 bits per second. 

The bit rate had jumped four-fold because, well, competition. Prices dropped and by the late 1970s microcomputers were showing up in homes. There was a modem for the S-100 Altair bus, the Apple II through a Z-80 SoftCard, and even for the Commodore PET. And people wanted to talk to one another. TCP had been developed in 1974 but at this point the most common way to communicate was to dial directly into bulletin board services. 

1981 was a pivotal year. A few things happened that were not yet connected at the time. The National Science Foundation created the Computer Science Network, or CSNET, which would result in NSFNET later, and when combined with the other nets, the Internet, replacing ARPANET. 

1981 also saw the release of the Commodore VIC-20 and TRS-80. This led to more and more computers in homes and more people wanting to connect with those online services. Later models would have modems.

1981 also saw the release of the Hayes Smartmodem. This was a physical box that connected to the computer of a serial port. The Smartmodem had a controller that recognized commands. And established the Hayes command set standard that would be used to connect to phone lines, allowing you to initiate a call, dial a number, answer a call, and hang up. Without lifting a handset and placing it on a modem. On the inside it was still 300-baud but the progress and innovations were speeding up. And it didn’t seem like a huge deal. 

The online services were starting to grow. The French Minitel service was released commercially in 1982. The first BBS that would become Fidonet showed up in 1983. Various encoding techniques started to come along and by 1984 you had the Trailblazer modem, at over 18,000 bits a second. But, this was for specific uses and combined 36 bit/second channels. 

The use of email started to increase and the needs for even more speed. We got the ability to connect two USRobotics modems in the mid-80s to run at 2400 bits per second. But Gottfried Ungerboeck would publish a paper defining a theory of information coding and add parity checking at about the time we got echo suppression. This allowed us to jump to 9600 bits in the late 80s. 

All of these vendors releasing all of this resulted in the v.21 standard in 1989 from the  ITU Telecommunication Standardization Sector (ITU-T). They’re the ones that ratify a lot of standards, like x.509 or MP4. Several other v dot standards would come along as well. 

The next jump came with the SupraFaXModem with Rockwell chips, which was released in 1992. And USRobotics brought us to 16,800 bits per second but with errors. But we got v.32 in 1991 to get to 14.4 - now we were talking in kilobits! Then 19.2 in 1993, 28.8 in 1994, 33.6 in 1996. By 1999 we got the last of the major updates, v.90 which got us to 56k. At this point, most homes in the US at least had computers and were going online. 

The same year, ANSI ratified ADSL, or Asymmetric Digital Subscriber Lines. Suddenly we were communicating in the megabits. And the dial-up modem began to be used a little less and less. In 2004 Multimedia over Coax Alliance was formed and cable modems became standard. The combination of DSL and cable modems has now all but removed the need for dial up modems. Given the pervasiveness of cell phones, today, as few as 20% of homes in the US have a phone line any more. We’ve moved on.

But the journey of the dial-up modem was a key contributor to us getting from a lot of disconnected computers to… The Internet as we know it today. So thank you to everyone involved, from Ma Bell, to Rockwell, to USRobotics, to Hayes, and so on. And thank you, listeners, for tuning in to this episode of the History of Computing Podcast. We are so lucky to have you. Have a great day.