Wikipedia
In computing, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer A driver provides a software interface to hardware devices, enabling operating systems and other computer programs to access hardware functions without needing to know precise details about the hardware being used A driver communicates with the device through the computer bus or communications subsystem to which the hardware connects When a calling program invokes a routine in the driver, the driver issues commands to the device Once the device sends data back to the driver, the driver may invoke routines in the original calling program
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