They're talking about wavelengths ("per cycle"). But I'm not sure it makes more sense knowing that, since there's a fundamental disconnect between the signal frequency and the carrier frequency. I think QAM can even be used on a signal rate that's higher than the carrier frequency (as long as the carrier frequency is known), but I'm not 100% sure.
If we take our definition of "individual computing module" to be that it has a defined state during every tick of the clock, then there is a hard physical limit of 30cm for a module that runs at 10ghz. Anything larger must be operating asynchronously, as a distributed system.
Point is that interconnect between floor 1 and 5 might pose considerable challenges, thus greatly minimizing the potential advantages of having massive building sized computers
