Hayes AT command set
specific command language originally developed by Dennis Hayes for the Hayes Smartmodem 300 baud modem in 1981
The Hayes command set (also known as the AT command set) is a specific command language originally developed by Dale Heatherington and Dennis Hayes for the Hayes Smartmodem in 1981.
The command set consists of a series of short text strings that can be combined to produce commands for operations such as dialing, hanging up, and changing the parameters of the connection. The vast majority of dial-up modems use the Hayes command set in numerous variations.
The command set covered only those operations supported by the earliest 300 bit/s modems. When new commands were required to control additional functionality in higher-speed modems, a variety of one-off standards emerged from each of the major vendors. These continued to share the basic command structure and syntax, but added any number of new commands using some sort of prefix character – & for Hayes and USRobotics, and \ for Microcom, for instance. Many of these were re-standardized on the Hayes extensions after the introduction of the SupraFAXModem 14400 and the market consolidation that followed.
The term Hayes compatible was and as of 2018 still is important within the industry.
History
Background
Before the introduction of the bulletin board system (BBS), modems typically operated on direct-dial telephone lines that began and ended with a known modem at each end. The modems operated in either "originate" or "answer" modes, manually switching between two sets of frequencies for data transfer.
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Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Sep 6, 2026. The linked authority identifier is Q298684. None of the 1 selected statements returned an explicit reference. The first chronological checks are 1981 and 2018.
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This entry incorporates text from “Hayes AT command set” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.