On 386 mainboards (at least on the ones I have, or have had so far) the CPU frequency is half of the frequency of the oscillator installed on the board. On some boards there is also a socket for a second oscillator, intended for a math coprocessor of a different frequency than that of the CPU. The question is: does the same "1/2" rule apply in this case? I mean, in order to install a 33MHz NPU do I need a 66MHz oscillator?