History of Hayes Modem

Fascinating facts about the invention of the PC Modem by Dennis Hayes in 1977


Modem, device that converts between analog and digital signals. Digital signals, which are used by computers, are made up of separate units, usually represented by a series of 1's and 0's. Analog signals vary continuously; an example of an analog signal is a sound wave. Modems are often used to enable computers to communicate with each other across telephone lines. A modem converts the digital signals of the sending computer to analog signals that can be transmitted through telephone lines. When the signal reaches its destination, another modem reconstructs the original digital signal, which is processed by the receiving computer. If both modems can transmit data to each other simultaneously, the modems are operating in full duplex mode; if only one modem can transmit at a time, the modems are operating in half duplex mode.

To convert a digital signal to an analog one, the modem generates a carrier wave and modulates it according to the digital signal. The kind of modulation used depends on the application and the speed of operation for which the modem is designed. For example, many high-speed modems use a combination of amplitude modulation, where the amplitude of the carrier wave is changed to encode the digital information, and phase modulation, where the phase of the carrier wave is changed to encode the digital information. The process of receiving the analog signal and converting it back to a digital signal is called demodulation. The word "modem" is a contraction of its two basic functions: modulation and demodulation.

Dennis C. Hayes invented the PC modem in 1977, establishing the critical technology that allowed today's online and Internet industries to emerge and grow.

He sold the first Hayes modem products to computer hobbyists in April of 1977 and founded D.C. Hayes Associates, Inc., the company known today as Hayes Corp., in January of 1978. Hayes quality and innovation resulted in performance enhancements and cost reductions that led the industry in the conversion from leased line modems to intelligent dial modems -- the PC Modem.

Hayes-Compatible, in computer science, an adjective used to describe a modem that responds to the same set of commands as a modem manufactured by Hayes Microcomputer Products, originators of the de facto standard for microcomputer modems.


RELATED INFORMATION: Dennis C Hayes, Inventor Profile from The Great Idea Finder History of Computing from The Great Idea Finder

ON THE WEB: Zoom Telephonics, Inc. This company acquired most of the modem assets of Hayes Corporation. (URL http://

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The Rise and Fall of the Modem King Dennis C. Hayes begins selling personal computer modem products to computer hobbyists. Initially, the modems are boards for the S-100 bus, and later for the Apple II. International Herald Tribune. Article by Victoria Shannon. (URL http:// timeline.textfiles.com/1977/ )

Hayes Compatible

There was a time when Hayes compatible meant something. (URL http://

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Modem Standards

The organization that now sets modem standards is the International Telecommunication Union. (URL:

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Computer History

Timeline of computer history from BC to the present. Presented by Computer Hope, free help for computer users.History for 1960 - 1980 (URL

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Buzz Words

A Glossary of Modem Terms (URL

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Modems (This site has closed.)

The latest, and last, analog modem standard is called v.90, and everything you ever wanted to know about modems. (URL

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Modem pioneer struggles for survival (Article removed.)

The company is offering a new product -- a limited-edition, 56K

20th anniversary modem, signed by Dennis Hayess. Article from USA TODAY, by The Associated Press. (URL
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How Modems Work

From the popular How Stuff Works Web site by Marshall Brain. Lots of COOKIES and POP-UP ADS at this site.


a.. 1978 -- Dennis C. Hayes and partner Dale Heatherington, working on Hayes' dining room table, develop first personal-computer modem and formed a company.

b.. 1985 -- Hayes annual sales hit $120 million as popularity of home computers grows.

Reference Sources in BOLD Type This page revised March, 2005.

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