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Fascinating facts about the invention of the PC Modem by Dennis Hayes and Dale Heatherington in 1977. PC MODEM
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 and Dale Heatherington invented the PC modem in 1977, establishing the critical technology that allowed today's online and Internet industries to emerge and grow.

They 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.


History of Computing   from The Great Idea Finder

Zoom Telephonics, Inc.
This company acquired most of the modem assets of Hayes Corporation.

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.

CRN Industry Hall Of Fame
As USIIA chairman, Hayes advocates effective Internet policy, a role born from his invention of the PC modem in the late 1970s. CMP article by Michele Pepe.
Hayes Compatible
There was a time when Hayes compatible meant something.

Modem Standards
The organization that now sets modem standards is the International Telecommunication Union.
Computer History
Timeline of computer history from BC to the present. Presented by Computer Hope, free help for computer users.History for 1960 - 1980


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


  • 1978 -- Dennis C. Hayes and partner Dale Heatherington, working on Hayes’ dining room table, develop first personal-computer modem and formed a company.
  • 1985 -- Hayes annual sales hit $120 million as popularity of home computers grows.
  • 1988 -- Hayes and first wife Melita divorce after six years of marriage.
  • 1994 -- Hayes Microcomputer files for Chapter 11 bankruptcy reorganization.
  • 1996 -- Company emerges from Chapter 11.
  • 1997 -- Company merges with Access Beyond of Gaithersburg, Md.
  • 1998 -- Hayes Corp. files for Chapter 11.
  • 1999 -- January 6, Hayes shuts down Its operations.
  • 1999 -- April. 7, Zoom Telephonics Acquires Hayes Modem Assets Source: Hayes Corp
Reference Sources in BOLD Type This page revised January 24, 2006.

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