Hayes AT Commands Still Control 40-Year-Old Tech

The Hayes AT command set, developed by Dale Heatherington and Dennis Hayes in 1981, is a specific command language used for controlling dial-up modems. The command set was initially developed for the Hayes Smartmodem and consists of a series of short text strings that can be combined to produce commands for various operations.

The Hayes command set covered only those operations supported by the earliest bit/s modems. However, as new commands were required to control additional functionality in higher-speed modems, various one-off standards emerged from major vendors. These standards shared the basic command structure and syntax but added new commands using prefix characters.

The vast majority of dial-up modems use the Hayes command set in numerous variations. The command set has undergone re-standardization, particularly after the introduction of the SupraFAXModem 14400, which led to market consolidation. The originating modem operates at frequencies of 1,270 Hz (Mark tone, Binary 1) and 1,070 Hz (Space tone, Binary 0), while the answering modem operates at frequencies of 2,225 Hz (Mark tone) and 2025 Hz (Space tone).

## Why it matters The Hayes AT command set has played a significant role in the development of dial-up modems. Its widespread adoption has ensured compatibility across different devices and vendors, facilitating communication and data transfer. The command set's impact can still be seen in the numerous variations used today, a testament to its enduring influence on the technology industry.

The Hayes command set has become an essential component of dial-up modems, enabling users to control various operations such as dialing, hanging up, and changing connection parameters. Its development and evolution have contributed to the growth of the technology industry, and its legacy continues to be felt in the modern digital landscape.