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The RS-449 specification, also known as EIA-449 or TIA-449, defines the functional and mechanical characteristics of the interface between data terminal equipment, typically a computer, and data communications equipment, typically a modem or terminal server. The full title of the standard is EIA-449 General Purpose 37-Position and 9-Position Interface for Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange.
449 was part of an effort to replace RS-232C, offering much higher performance and longer cable lengths while using the same DB-25 connectors. This was initially split into two closely related efforts, RS-422 and RS-423. As feature creep set in, the number of required pins began to grow beyond what a DB-25 could handle, and the RS-449 effort started to define a new connector.
449 emerged as an unwieldy system using a large DC-37 connector along with a separate DE-9 connector if the 422 protocol was used. The resulting cable mess was already dismissed as hopeless before the standard was even finalized. The effort was eventually abandoned in favor of RS-530, which used a single DB-25 connector.