This is the device driver for serial port 1:
Is there a device driver for a USB port, or does USB works in a much complicated way that a USB port can't be represented using a single file?
/dev/ttyS1 is a device node for the second serial port.
USB serial ports also get device nodes, they’re usually called
/dev/ttyUSB0 and so on. Some USB devices will allocate two nodes (e.g.
/dev/ttyUSB1; old USB Palm devices do this). Some USB serial devices which act more like a modem will have a
/dev/ttyACM0 device node instead.
The actual device drivers are in the kernel, often provided as kernel modules. On PCs using 8250-style serial ports, the driver is
tty/serial/8250/serial_cs.ko. For USB serial ports, it will be one of the drivers in
usb/serial. (Both paths are relative to