COM ports, short for communication ports, are traditional serial port interfaces on IBM PC-compatible computers. They refers not only to physical ports, but also to virtual ports such as ports created by Bluetooth or USB-to-Serial adapters.

USB-to-Serial adapters do two things:

1. They physically connect a serial cable to a USB port.

2. They have software drivers that create a Virtual COM Port.

A Virtual COM Port created by a USB-to-serial adapter can be a setting that allows software products to connect to USB devices using COM port connections.

A serial port (串行接口) is a serial communication interface through which information transfer in or out one bit at a time. Throughout most of the history of personal computers, data was transferred through serial ports to devices such as modems (调制解调器), terminals (终端机) and various of peripherals (外部设备). Serial ports are still used in applications such as industrial automation system, scientific instruments as they are simple, cheap and their console (控制) functions are highly standardized and widespread. A serial port requires very little supporting software from the host system. Modern computers without serial ports may require USB-to-Serial adapters to allow compatibility with serial devices.

A parallel port (并行接口) is a parallel communication physical interface, which is also known as a printer port or Centronics port. It was originally known as the Parallel Printer Adapter on IMB PC-compatible computers as it was primarily designed to operate printers. Today, the parallel port is virtually non-existent because of the rise of USB devices.

Universal Serial Bus (USB,通用串行总线) is an industry standard that defines the cables, connectors and communication protocols used in a bus (a bus/buss is a communication system that transfer data between components inside a computer or between computers) or connection, communication and power supply between computers and electronic devices. It was designed to standardize the connection of computer peripherals including keyboard, pointing devices, digital cameras, printers, portable media players, disk drives and network adapters to PC, both to communicate and to supply electric power.

A device file is an interface for a device driver that appears in a file system as if it were an ordinary file. They allow software to interact with a device driver using standard input/output (I/O) system calls, which simplifies many tasks and unifies user-space I/O mechanisms. Device files often provide simple interfaces to peripheral devices such as printers and serial ports. Also, they can be used to access specific resources on those devices. Finally, device files are useful for accessing system resources that have no connection with any actual device.