A UART (Universal Asynchronous Receiver/Transmitter) Sub Device Windows driver is typically used to manage communication between a computer and a UART-based device, often via a serial port (COM port). UART is a hardware communication protocol commonly used for low-speed, short-distance communication between devices such as microcontrollers, sensors, or other peripherals.

In the context of a UART Sub Device, the driver facilitates the communication with a specific UART-enabled device, often one that is embedded within another device or an add-on (e.g., a USB-to-UART adapter, Bluetooth serial device, or a custom embedded system). The term "Sub Device" may imply that the UART functionality is part of a larger device or system.