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The people who are saying that Wifi works faster on 5GHz because the frequency of the carrier wave is faster than 2.4GHz (“5 is bigger than 2, so it must be better, right?”) are right, but not for the reasons that they think they are. We’re not talking about CPU clock speeds here, we’re talking about radio frequencies.
The unmodulated wave has a higher frequency, yes. However. that would only allow it to carry more information if the device had unfettered access to the entire spectrum of frequencies up to and including 5GHz. But it doesn’t - we divide the wireless spectrum into many, many bands so that different uses can be accommodated without interfering with each other, which means we have to figure out how to squeeze the data we want to send into narrow channels, The information being transmitted is all carried in the differences between a modulated wave and the unmodulated carrier. In other words, slight frequency, amplitude, and phase variations are what gets interpreted as data. As a result, what frequency is used as the carrier isn’t the key factor in its performance, it’s the available width around the chosen carrier frequency that matters. This is a critical point - If I get 20MHz of space to play with in a channel, it doesn’t matter whether that 20MHz is centered around something in the 2.4 or 5GHz range. (With some small exceptions - which we’ll get to in a moment.) This is just like radio and TV channels, which live at different frequencies offset from each other to avoid interfering. Channel 5 didn’t get better quality than channel 2 by being centered on a higher frequency.
The actual reasons for the large differences in performance between these two bands have to do with the newer Wifi standards being able to squeeze more information into a given chunk of radio spectrum than the older ones, as well as less crowding of the available channels.
In 2.4GHz Wifi, most of the available channels overlap each other, which means that lots of devices are fighting for the same few narrow 20MHz channels. In the US, the only way to avoid overlap is to only use 3 channels (1, 6, and 11) which do not overlap with each other. Anyone nearby using any of the other channels still causes interference, regardless.
In 5GHz Wifi, there are more channels available, none of them overlap with each other at all, and each channel is allocated twice as much bandwidth than any of the 2.4GHz channels. Because the 5GHz channels are wider, the newer Wifi standards like 802.11ac use more densely packed modulation schemes (more combinations of altered phase/frequency/amplitude are recognized), as well as a trick of using multiple simultaneous streams on multiple channels. This increases the amount of data that can be transmitted simultaneously between devices, and the standard only uses these techniques in the 5GHz band. In fact, 802.11ac ONLY uses 5GHz, and gave up completely on operating in the 2.4 band at all. 802.11n (an earlier version) used some of these techniques to a limited degree in the 2.4GHz band, but the lack of non-overlapping channels and interference from other devices limited its effectiveness and maximum theoretical speed, as compared to doing the same on the 5Ghz channels.
Finally, there's the fact that there are just generally less devices overall using 5GHz (no Bluetooth, no telephones, microwave ovens, etc.), which leads to less local interference. So while it's true that 5GHz doesn't carry as effectively through walls, the existing standards do allow for much higher throughput in that band. And since in most residential environments, the walls attenuate the signals more dramatically than with 2.4GHz, that also contributes to less interference from your neighbors.
As I hope you can see, there’s a lot more to it than “5GHz is a higher frequency than 2.4GHz.”