Function Key Toggle Apple Keyboard.

For Windows using the Apple USB keyboard without Bootcamp Control Panel software i.e. you aren’t using a Mac but still want to use the APPLE SUB Keyboard. Open the Registry and search for the following Key:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\KeyMagic 

Find the entry

OSXFnBehavior

Change the value from 01 to 00

00 is Function Keys

01 is Media Keys

Unplug the keyboard or restart the computer to reload the new value.