ANS:A - serial ports

RS-232 (or Recommended Standard 232) is a standard computer communications system that's more commonly known as a serial connection. It is, however, often used for connecting A/V components to automation and control systems (such as touchpads and controllers.

RS232 is an asynchronous communication protocol. More formally RS232 is an asynchronous communication protocol that lets you transfer data between electronic devices. Basically it can transfer a single byte of data over a serial cable having between 3 to 22 signals and running at speeds from 100 to 20k baud.