Temperature and Voltage...

hitechjb1 said:

Effect of die temperature on CPU clock frequency at a given Vcore
For a given Vcore, die temp does make a difference, can be a big difference.

E.g. for the same Vcore 1.9V on a Tbred B 1700+ DLT3C, roughly speaking,
- a difference of 10 C would enable one to clock about 4% faster, which is roughly 100 MHz at 2500 MHz.
- If there is a 50 C difference in die temp, e.g. one at 50 C on air, one at 0 C using extreme cooling, at same Vcore, the CPU at 0C would be able to run at about 20% faster, which is about 500 MHz more, compared to the one at 2.5 GHz on air.

Reason: electrons move faster at lower temperature under same voltage.

Click to expand...

hitechjb1 said:

How much voltage can be applied to a CPU

There are two components of power going into a CPU at a given Vcore:

1. The "good" CV^2f active power which powers the CPU to run at frequency f.
2. The "wasted" V^2/R static power which biases the CPU as leakage current, but also heats up the chip.

Putting in higher Vcore would generally let you clock faster (CVcore^2f). But unfortunately, it also heats up the chip (Vcore^2/R).

So on air, at lower temperature 10-20-30 C, the CPU can be clocked faster and faster at a rate about 130-140 MHz/100mV (for Tbred B, Barton). So far so good. But at the same time, the chip will begin to heat up due to Vcore increases (the V^2/R compoent and also from the active CV^2f component). As a result of heat, the electrons move slower inside the chip and the CPU begin to run slower, the above rate delf/delVcore begins to drop to 120 then 110 then 100 then 50 MHz /100 mV when die temperature reaches beyond 30 C, 40 C, 50 C, ... correspondingly for Vcore above 1.7, 1.8, 1.9 V, ... The heat increases at a rate faster than the Vcore increase to slow down the chip.

This is what we call the diminishing return on CPU frequency. And eventually, around 1.95 - 2 V for Tbred B, 1700+ DLT3C, it will come to "stop" (due to heat, high current and system instability) even when more Vcore is put in, since the heat slows the chip down. There is no more reason to increase Vcore anymore (even you don't kill the chip). For higher Vcore rated ones such as 2100+, Barton 2500+, that Vcore wall is around 2.05 - 2.2 V on air.

The above numbers are mainly for illustration, and they are roughly correct. But don't quote and use them for exact calculation.

If you use thermoelectric, phase change, .... exterme cooling, due to the lower die temperature, as mentioned above, the chips can run much faster and reach much higher frequency (e.g. 3+ GHz) at the same Vcore (compared to air/water) before the die reaching the higher temperature as cooled by air. E.g. at 1.95-2V 1700+ will run at 2.5-2.6 GHz on air at 50 C, but it will run at 3 - 3.2 GHz at -10 C.

It does not mean you can put much higher Vcore onto the chips at lower die temperature. Vcore is subjected to transistor leakage increase, gate breakdown constraints. They run faster is a combination of higher active power to substain the computation (both logical and electrical) and lower die temperature, not higher Vcore alone.

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c627627 said:

Gotta love hitechjb1's involved posts backed up with data.

How about this:
It has been said that all T-Bred A's average 2.0 GHz while all T-Bred B's average 2.3 GHz.

Of course the numbers vary from system to system but if we were to talk in general average terms, what then would be the highest acceptable temperature where the term acceptable is defined in hitechjb1's previous post.

Click to expand...

c627627 said:

Gotta love hitechjb1's involved posts backed up with data.

How about this:
It has been said that all T-Bred A's average 2.0 GHz while all T-Bred B's average 2.3 GHz.

Of course the numbers vary from system to system but if we were to talk in general average terms, what then would be the highest acceptable temperature where the term acceptable is defined in hitechjb1's previous post.

Click to expand...