A multi serial port card is a device that can allocate multiple serial/parallel ports for terminal connections, allowing each terminal to communicate with the host through it. Using a multi-user card is the most convenient and simple solution to expanding the number of external devices on a computer. It can facilitate the expansion of serial or parallel ports on computers, so it is also known as a serial parallel port expansion card.

There are two types of multi serial port cards, one can be inserted into a PCI slot and can expand 1-4 serial ports. After installing the driver, com3, come4, etc. can be seen in the device manager Another option is to connect it to the network, which allows multiple computers to share the serial port resources on it, but the configuration is more complicated.

Especially suitable for multi-user operating systems such as UNIX and LINUX, and also applicable to operating environments such as WINDOWS95/98/2000, WINDOWS NT, DOS, etc. Multi user cards are widely used in banking, finance, securities, power lines, industrial control and other fields, and are an important hardware component of computer multi-user communication control systems.