Editing Hayes AT command set (section)

=== Compatibility ===
While the original Hayes command set represented a huge leap forward in modem-based communications, with time many problems set in, almost none of them due to Hayes ''per se'':
* Due to the lack of a written standard, other modem manufacturers just copied the external visible commands and (roughly) the basic actions. This led to a wide variety of subtle differences in how modems changed from state to state, and how they handled error conditions, hangups, and timeouts.
* Each manufacturer tended to add new commands to handle emerging needs, often incompatible with other modems. For example, setting up hardware or software handshaking often required many different commands for different modems. This undermined the handy universality of the basic '''Hayes command set'''.
* Many '''Hayes compatible''' modems had serious quirks that made them effectively incompatible. For example, many modems required a pause of several seconds after receiving the "AT Z" reset command. Some modems required spaces between commands, while others did not. Some would unhelpfully change baud-rate of their own volition, which would leave the computer with no clue how to handle the incoming data.

As a result of all this, eventually many communications programs had to give up any sense of being able to talk to all "Hayes-compatible" modems, and instead the programs had to try to determine the modem type from its responses, or provide the user with some option whereby they could enter whatever special commands it took to coerce their particular modem into acting properly.