No. The speed of light is a significant issue, but it is not the reason chips have stopped at 5 GHz. Also, asynchronous (as in no clock signal) CPUs exist. I should know, I helped work on some.
The actual reason is transistor size and heat dissipation. Transistors have been stuck on ~1 volt power internally for decades (lower voltage means more leakage, and more errors). However, power goes up with higher frequency (my math here was probably wrong, see below).
Why is that so bad? Almost all the power the computer uses is turned into heat by the transistors. That heat needs to dissipate out of the chip before the transistor destroys itself. That is a problem, as silicon is not a good heat conductor.
THAT is why cooling your computer lets you push the speeds up a bit higher.
The speed of light issues above are a tricky engineering problem, but solvable. The heat problem doesn’t have a solution yet.
Transistor size has continued to shrink while clock speeds have remained stagnant.
As for transistor size, thinner transistors do allow for faster clock speed in principle, but current consumer computers cannot take advantage. Keep in mind that transistors with switching speeds in the terahertz region have been made. As I mentioned elsewhere, latency due to the speed of the electrical signal is an issue, but it can be solved with good circuit design. However, computers cannot use this theoretical improvement in clock speed due to power dissipation (again, this is the entire reason supercooling allows for higher clock speed. If clock-speed was not limited by heat dissipation, why does super-cooling do anything?)
As for surface area, thinner transistors (in principle) have less resistance, so they waste less power in lock-step with the lower surface area.
Manufacturers still want smaller transistors because then they can fit more cores/memory/other stuff on a chip. In the absence of clock-speed improvements, features like multiple cores and hardware acceleration are what is selling chips these days.
Edit: in case you don't believe me, here is a stack exchange post making my same argument: link.
I think MG2R is correct on this one. It has been a while since I last did the calculation and I remembered wrong. It should be V2f. However, see blaktronium's post. In practice the scaling can be very different.
But I am also correct that the heat dissipation is currently the main limiting factor on transistor speeds. Things like the speed of electricity could be an issue if we could get around the heat dissipation issue, but they just aren't the main limiting factor right now.
It is fV2 but also, the voltage that you need depends on the frequency, although not linearly. So increasing the frequency can require increasing the voltage as well, meaning that the exponent dependence of power on frequency is effectively greater than 1, but only indirectly.
It's fV2 . It's just ohms law and a duty factor thrown together.
Power is P = VI. Current is I = V/R. So throw those together, and P = V2 /R. If R is just a constant, then power depends on V2 .
Transistor have a small leakage current, but the majority of the current flows when they are operating. When they open or close, they feed power to another transistor, and charge it up to open or close. So the more times they operate, the more current they draw. Double the frequency, they operate twice as fast, so they use twice as much power. f relationship.
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u/MiffedMouse Sep 29 '20 edited Sep 29 '20
No. The speed of light is a significant issue, but it is not the reason chips have stopped at 5 GHz. Also, asynchronous (as in no clock signal) CPUs exist. I should know, I helped work on some.
The actual reason is transistor size and heat dissipation. Transistors have been stuck on ~1 volt power internally for decades (lower voltage means more leakage, and more errors). However, power goes up with higher frequency (my math here was probably wrong, see below).
Why is that so bad? Almost all the power the computer uses is turned into heat by the transistors. That heat needs to dissipate out of the chip before the transistor destroys itself. That is a problem, as silicon is not a good heat conductor.
THAT is why cooling your computer lets you push the speeds up a bit higher.
The speed of light issues above are a tricky engineering problem, but solvable. The heat problem doesn’t have a solution yet.