For example, the COM port of PCI expansion card is extended to two RS232 ports. See the figure below.

If you need to control at the same time, you can use the HUB2232Z * * exclusive device. See the figure below.

There is even a multi-serial card, which is a device that can allocate multiple serial ports/parallel ports to connect terminals, and each terminal can communicate with the host through it. Using multi-user card is the most convenient and simple solution to expand the number of computer external devices. It can make the computer conveniently expand serial port or parallel port, so it is also called serial-parallel port expansion card. See below.