Implementations of serial ports

While interfaces such as Ethernet or USB send data as a serial stream, the term serial port usually identifies hardware compliant to the RS-232 or RS-422/RS-485 standard.

In modern computers, serial ports have been replaced by USB-to-serial devices due to the fact that a RS-232 port can be easily emulated by a dedicated USB device. However, standard serial ports hardware still exists in the embedded and industrial world. The reason is quite simple: serial ports are easy to use and easy to implement (they require little supporting software from the CPU). So, serial ports are still used in applications such as industrial automation systems and remote monitoring or in some scientific instruments. It's quite easy to find industrial devices (not only a normal peripheral, but just a complete system) that use one or more serial ports to communicate with other systems.

As already stated, the most used serial port implementations are RS-232, RS-422, and RS-485. RS-232...