Driver on XP without inf file

I am working on a project to create a tool that helps migrate legacy Windows applications from XP and other Windows operating systems.

Part of this work is to identify drivers that are installed with the application.

I am looking at an application and driver that are installed on Windows XP SP3.

The driver is listed in device manager under Non-Plug and Play Drivers as NetworkX.

Running sc query type= driver shows:

SERVICE_NAME: NetworkX
DISPLAY_NAME: NetworkX
        TYPE               : 1  KERNEL_DRIVER 
        STATE              : 4  RUNNING 
                                (STOPPABLE,NOT_PAUSABLE,IGNORES_SHUTDOWN)
        WIN32_EXIT_CODE    : 0  (0x0)
        SERVICE_EXIT_CODE  : 0  (0x0)
        CHECKPOINT         : 0x0
        WAIT_HINT          : 0x0

The registry key

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NetworkX

contains an ImagePath data value of \SystemRoot\system32\ckldrv.sys. This association is confirmed by using msinfo32 under Software Environment > System Drivers.

I was interested to have a look at the associated inf file, but here's the thing: I can find no inf file for this driver on the system anywhere.

I was under the impression that in order to install a driver, it is necessary to have an inf file.

How is it possible to install a driver on a system without an inf file?