Most of the operating system code is dedicated to managing input and output.
An I/O device is connected to the machine via I/O port. Like usb,hdmi,serial ports. Each input output device has a controller that maintains local buffer storage and special purpose registers.
The device controller is nothing but intermediate hardware between the machine, device and OS. The OS → CPU → device controller.
The only way the CPU can communicate with the device manager is by talking to the device driver.
Driver and OS are both loaded on the same memory, but they are not part of each other
The driver and OS can both receive and send data to each other.
You can think of a driver as a daemon(background) program, which resides in the memory space until the system shuts down.
Above all, is why I/O devices (those shiny RGB keyboards) stop working as soon as driver program crashes.