The standard recommends the D-subminiature 25-pin connector up to revision C, and makes it mandatory as of revision D. Most devices only implement a few of the twenty signals specified in the standard, so connectors and cables with fewer pins are sufficient for most connections, more compact, and less expensive. Personal computer manufacturers replaced the DB-25M connector with the smaller DE-9M connector. This connector, with a different pinout (see Serial port pinouts), is prevalent for personal computers and associated devices.
the standard recommends the d-subminiature 25-pin connector up to revision c and makes it mandatory as of revision d most devices only implement a few of the twenty signals specified in the standard so connectors and cables with fewer pins are sufficient for most connections more compact and less expensive personal computer manufacturers replaced the db-25m connector with the smaller de-9m connector this connector with a different pinout (see serial port pinouts) is prevalent for personal computers and associated devices