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. Background During the late 1970s, the EIA began developing two new serial data standards to replace RS-232. RS-232 had a number of issues that limited its performance and practicality. Among these was the relatively large voltages used for signalling, +5 and -5V for mark and space. To supply these, a +12V power supply was typically required, which made it somewhat difficult to implement in a market that was rapidly being dominated by +5/0V transistor-transistor logic (TTL) circuitry and even lower-voltage CMOS implementations. These high voltages and unbalanced communications also resulted in relatively short cable lengths, nominally set to a maximum of , although in practice they could be somewhat longer if running at slower speeds. The reason for the large voltages was due to ground voltages. RS-232 included both a protective ground and a signal ground in the standard, but did not define how these were to be implemented. It was often the case that the protective ground was left unconnected, and the signal ground was connected to ground at both ends. As a result, if there was a slight difference in ground potential at the two ends of the cable, the voltage in the signal ground pin might not be zero, and large signal voltages were needed to provide a positive signal in this case. To address this problem, the