RS-449

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.

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.

These high voltages and unbalanced communications also resulted in relatively short cable lengths, nominally set to a maximum of 50 feet (15 m), although in practice they could be somewhat longer if running at slower speeds.

Along with other changes, the number of connections began to grow, to the point where even RS-423, which was functionally similar to RS-232, no longer fit in a DB25 connector.

This led to the use of the larger DC-37, but even that did not have enough pins to support RS-422, so this was "solved" by adding the additional ground wires to a separate DE-9 connector.