The Hayes Code

The obscure command set that gradually helped us move past acoustic couplers and brought dial-up modems into the mainstream. For a while, at least.

By Ernie Smith

Today in Tedium: Many parts of the computing experience may be outdated, but they haven’t become impossible to use. Old machines still turn on when you plug them in, after all, as long as Most of the time, the replaced devices maintain a prominent role among collectors, or at the very least some level of modern day usability. But dial-up modems represent an interesting case in the world of collecting. After all, many people don’t really use phone lines in the modern day, and in fact the whole system is slowly being dismantled after the Federal Communications Commission shifted requirements around copper phone lines, which will likely have the effect of pushing everyone to wireless lines or voice-over-IP solutions. In other words, the modem—as well as important modem analogues like DSL and ISDN—might quickly prove useless for many people. In other words, no more screechy sound from dialing up an ISP. Today’s Tedium takes a second to document two important aspects of the dial-up modem—the acoustic coupler and the Hayes command set—before they’re forgotten entirely. — Ernie @ Tedium

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The common nickname for the copper-line phone system, standing for “plain old telephone service.” This system, which has been active in one form or another since 1876, had to be managed by phone companies under the rulemaking of the FCC, but as alternative technologies have come into play, the commission has ended requirements that require POTS lines to be available for resale to businesses—giving telecom companies the opportunity to push legacy cases off its networks. While it’s not as dramatic as “POTS is going away tomorrow,” it nonetheless means that POTS system may fall out of complete use sooner rather than later as its commercial uses gradually dry up.

Acoustic Coupler Modem

An Atari 800XL, shown with an acoustic coupler modem. (Wolfgang Stief/Flickr)

How modems lost their acoustic couplers

As you may remember from my piece about how the Deaf community actually did the legwork that gave us some key modem-adjacent technologies (nearly four years old! I’ve been doing this a long time), one of the key elements of early modems was the acoustic coupler, a design that essentially was a hack.

The acoustic coupler was specifically designed to get around the phone system’s restrictions at the time, which prevented the use of “foreign attachments” until a regulatory ruling, the Carterfone decision, changed that.

But with the Carterfone decision on the books, a number of court decisions reaffirming the findings of that ruling, and the RJ11 modular jack first coming into use in the 1970s, the acoustic coupler was no longer necessary from a regulatory standpoint, even if the tooling still mattered for technical or even practical reasons.

In the 1970s, it was common for large machines, such as mainframes and minicomputers, to connect to the phone system directly without the use of an acoustic coupler, but at the microcomputer level, this situation was more complicated in part because there were so many of them, and these devices generally weren’t on standardized platforms.

But most computers of this age range did have something that was fairly standard—the RS-232 serial communications standard, which was already quite common on computers, and often relied on the same D-sub port style that was being adapted for video games during the same period.

And during the ’80s and ’90s, it was one factor that helped to shape the rise of the modem as an essential computing tool.

The other factor was Dennis Hayes. A onetime engineer for National Data Corporation who had experience working with AT&T’s Long Lines service, his job was actually setting up modems that made it possible for retailers to offer credit card machines. Those modems, built to connect to mainframes, didn’t need acoustic couplers, which meant that the job taught him a skill that would soon prove extremely valuable to the PC industry at large.

Hayes Micromodem

The Hayes Micromodem for the Apple II was extremely well-regarded in its time. The modem plugged into the system internally.

Eventually, the Georgia-based Hayes would get an itch that he and a coworker, Dale Heatherington, would scratch—the desire to make modems of their own outside of the confines of NDC. The company that they started, eventually called Hayes, made some of the first modems for microcomputers, which were included inside of the computer, utilizing the system’s internal bus. Hayes’ modems were successful right off the bat, earning the duo $125,000 within their first year ($573,000 with inflation added). Soon enough, their company was off to the races.

So why was Hayes so successful so quickly? According to a 1983 Atlanta Constitution profile, Hayes said that their modems came about at a time when computer accessories were relatively rare. After all, the computer retail industry had literally just started.

“In the early days, (computer) stores were hungry for something to sell,” he told the newspaper.

By emphasizing service, the company had earned an early reputation for high quality, and their internal modems didn’t need the acoustic coupler. That said, despite their advantages on machines like the Apple II, these modems left a significant gap in the market, something pointed out in a 1980 issue of Popular Electronics.

“As good as they are, the Hayes modems are system dependent and, consequently, leave the field open for competitors,” writer Carl Warren explained.

At the time, the PC industry was new. It had not standardized, and there were lots of computers with lots of incompatible technology. By building an internal modem, you were essentially making a bet that you were putting a device inside of the dominant player, at the expense of everyone else.

For a startup, this was a bad bet in the long term, and Hayes knew it. The way to go was clearly to build an accessory that could work on any machine. Utilizing RS-232 as its starting point, Hayes would quickly solve this, and create a legend in the process.


The number of people that were still using AOL’s dial-up service as of 2015, according to CNBC. However, that market had died off, and by the time the piece ran in 2021, the number was said to be “in the low thousands,” according to the business channel’s sources. Not that you would probably use it today, but AOL is still accessible through dialup, though, through the AOL Dialer service.

Smart Modem

The Hayes Smartmodem 300 went external because going external maximized compatibility. (Michael Pereckas/Wikimedia Commons)

A modem with a microprocessor—why the Hayes Smartmodem was such a groundbreaking device

In a sense, shedding the modem of its acoustic coupler was great because it allowed the device to go internal, but the fact of the matter is, external was really the way to go in the pre-standardization days, which meant that the modem really needed a design that could work across settings.

But by removing the coupler from the equation, it was harder to tell the modem what to do to ensure that, say, when you wanted to dial a number, it would have the good sense to do so. Essentially, modems not only needed a connection, but a way which they could control the process of connecting to an outside line.

Managing this internally was not so much a problem, because the modem had access to faster communication buses that allowed the machine to instruct it, but utilizing RS-232 connections that worked the same no matter the setting? That was hard. We were two decades off from USB. There was only so much room to transmit commands, and many microcomputer implementations of RS-232 actually removed certain capabilities as a cost-saving measure, meaning that there wasn’t a lot of room to push through dedicated commands.

Smart Modem manual

Hayes’ Smartmodem 300 manual, which included the Hayes command set. (via

Dennis Hayes and Dale Heatherington’s solution to this problem involved creating a primitive language of sorts that the terminal program could send to the modem, essentially by sending uncommon character combinations to the terminal program that it could understand.

One such command, an escape command generally represented by three characters (+++), swapped the modem between data and command mode, essentially telling the modem that it’s either managing a remote connection, or that commands are being sent directly to the modem. These commands, which were gradually expanded over the years, including by Hayes’ competitors, made it possible for any terminal program to work with the modem, which made the device hardware agnostic. As long as there was an accessible RS-232 port and a terminal that could directly speak to the modem, it was possible to make this external device work.

To manage this translation, the modem required a microprocessor, a small one, not a super-powerful one, but one that nonetheless made it so you didn’t have to put the receiver into an acoustic coupler.

Hence the name Smartmodem, which became the trademark name of Hayes’ famous computer modem line. For more than a decade, Hayes not only was the most prominent maker of modems, but it literally created the de facto standard by which people connected to bulletin boards or other similar services. It was the game port of modem protocols.

As other competitors emerged, including U.S. Robotics, 3Com, and Supra, these companies ended up using Hayes commands to manage their modem connections as well, albeit with some additions for their specific needs. Nonetheless, Hayes set up a plot with which modern computing was able to make a connection across a phone line in a much more automatic way than putting a phone on a coupler and hoping the result didn’t end up all garbled.

Hayes was by no means a perfect company—slow to adapt to faster baud speeds at a time when everyone wanted faster connections, undercut by cheaper and eventually built-in alternatives, and incorrectly betting on the mainstreaming of ISDN technology, the company barely limped its way through the 1990s before being acquired by its competitor Zoom Telephonics (no, not that Zoom).

(Hayes, the person, had his share of hard knocks, too—he was the subject of a very high-profile divorce during Hayes’ glory days, the settlement of which, around $40 million in 1980s money, was one of the largest in Georgia’s history.)

But even though Hayes, the company, no longer lives on, its command set remains the basis through which many dial-up modems communicate with their hosts today.

“At half the cost of less-capable modems from better-known competitors, the new Supra modem effectively crashed the modem market.”

— Kevin Driscoll, the author of a history of pre-internet social media called The Modem World, discussing the outsized impact the SupraFAXModem 14400 had on the modem industry in 1992. This model, which was faster than most of its competition and included fax capabilities, also sold for $399 at launch, which was absurdly cheap in comparison to anything else that fast on the market. In many ways, this may be one of the most important things to happen to computing during that period as it effectively started modems on the path to being commodities.

The water has long flowed under the bridge, but when I was a kid, getting a Hayes modem was both an important step for me and an important lesson.

On the occasion of my 13th birthday, I got one after having expressed deep interest in getting online, having read so much about this internet thing at the local library and seeing it on shows like Computer Chronicles. I wanted to experience how far I could get with this new thing I had received, this 2400-baud Hayes masterpiece.

I didn’t even get the real internet at first—I got CompuServe, AOL, and the ability to dial a bunch of BBSes. (I found the nonprofit organization near my home that could be freely dialed into that offered some semblance of the internet, but not the full-fat version. I treated dialing that line as a game—how far on the internet could I get with this limited connection? If I found a link using Lynx that opened up some broader search engine or list of links, I won.)

Within just a few months, my curiosity got the best of me, and I had called a bunch of long distance numbers to bulletin board services, including a BBS in Toronto that had RIP graphics. I had generated a $300 phone bill—and got grounded for it. I felt terrible, but let that curiosity throw me over the edge. I was a kid who never had a job before and apparently didn’t understand the value of a dollar!

But eventually, with that lesson learned, my parents figured out that the way to keep me in my own area code was the open internet, and they ended up purchasing an unlimited plan from a local ISP. It wasn’t even graphical at first—it was text-based, and we were embracing the ’net using a terminal program.

Eventually the Hayes modem would be replaced by something faster, but the device was iconic in its time. It was built like a tank, and even though its modern day use case is basically null and void, I have a strong affinity towards this device that not only got me on the internet for the first time, but that almost got me grounded for life.

On balance, it was totally worth it.


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Ernie Smith

Your time was just wasted by Ernie Smith

Ernie Smith is the editor of Tedium, and an active internet snarker. Between his many internet side projects, he finds time to hang out with his wife Cat, who's funnier than he is.

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