3 ms·

This is why CPUs aren't getting any faster: https://www.google.com/search?q=c+%2F+5+ghz https://www.google.com/search?q=c+%2F+5+ghz

morenoh149 13y ago
care to explain? I'm curious what you mean by that google search
- michael_nielsen 13y ago
  It means signals can only propagate about 6 centimeters during a single CPU clock cycle. That makes accessing information off-chip difficult in a single cycle, since 6 centimeters is on the same order as the linear scale of most motherboards. This limit doesn't immediately impact computations that are carried out entirely on-chip. I expect that's the great majority of computations on today's CPUs, which typically have large caches. So I'm not sure the GP's explanation is correct, although it's certainly interesting.
  - lotsofmangos 13y ago
    As an explanation for why you cant get clock speed increases of the same order of magnitude as you could previously, without changing the entire technology, it would seem correct. 6cm now means that you only need to double twice to get to less than the die width. Also, electricity does not propagate through copper at c, but at between 40% and 90% of it, depending on the inductance and capacitance of the circuit, so you are looking at even less of an increase before you start running into some really thorny problems as not only are you running up against relativistic limitations, but different bits of your chip can be doing it at noticeably different times.
- frakturfreund 13y ago
  Nothing can't travel faster than the speed of light – including Electric current. So in a hypothetic 5 gigahertz CPU, there couldn't be a path through the wires/transistors longer than 5.99584916 – otherwise, the end result couldn't be correctly determined. That's why CPU's got smaller and smaller. But since the transistor shrinking slows down, and Adders/Multiplyer/Register/Decoding Logic etc. all takes some time and length, it's harder to make a CPU with a shorter longest path.
Qantourisc 13y ago
This is actually less of an issue as you think it is. You can use asynchronous communication. But leaking 5GHz outside your cpu is a BAD idea.

morenoh149 13y ago

care to explain? I'm curious what you mean by that google search

michael_nielsen 13y ago
It means signals can only propagate about 6 centimeters during a single CPU clock cycle. That makes accessing information off-chip difficult in a single cycle, since 6 centimeters is on the same order as the linear scale of most motherboards. This limit doesn't immediately impact computations that are carried out entirely on-chip. I expect that's the great majority of computations on today's CPUs, which typically have large caches. So I'm not sure the GP's explanation is correct, although it's certainly interesting.
- lotsofmangos 13y ago
  As an explanation for why you cant get clock speed increases of the same order of magnitude as you could previously, without changing the entire technology, it would seem correct. 6cm now means that you only need to double twice to get to less than the die width. Also, electricity does not propagate through copper at c, but at between 40% and 90% of it, depending on the inductance and capacitance of the circuit, so you are looking at even less of an increase before you start running into some really thorny problems as not only are you running up against relativistic limitations, but different bits of your chip can be doing it at noticeably different times.
frakturfreund 13y ago
Nothing can't travel faster than the speed of light – including Electric current. So in a hypothetic 5 gigahertz CPU, there couldn't be a path through the wires/transistors longer than 5.99584916 – otherwise, the end result couldn't be correctly determined. That's why CPU's got smaller and smaller. But since the transistor shrinking slows down, and Adders/Multiplyer/Register/Decoding Logic etc. all takes some time and length, it's harder to make a CPU with a shorter longest path.

Qantourisc 13y ago

This is actually less of an issue as you think it is. You can use asynchronous communication. But leaking 5GHz outside your cpu is a BAD idea.