What is virtual com port?

A virtual port is a software emulation of a port which normally would be present in hardware. This is most commonly used with modems and printers.

Many internal modems emulate a COM port. When modems first became common by far the most common type was an external modem which plugged into a serial port (a COM port) in the back of the machine. Nearly all of the early dial-up networking applications were written with the assumption that the modem could be found on one of these COM ports. While it is no longer necessary for the modem to reside on a COM port, most new modems still emulate one in order to maintain compatibility with these legacy applications. Printers can also reside on a virtual port for much the same reasons. All printers used to plug into a parallel port (an LPT port) on the computer. As a result many legacy programs were written with the assumption that any printers would be located on an LPT port. When USB printers became commonplace it became necessary to allow these USB printers to be assigned a virtual parallel port in order to maintain compatibility with these older programs. This can be configured in the OS in the printers settings and is most often used for DOS-level point-of-sale or data-entry applications.