1800X: First Test Of Scaling With LN2
By luck, we chose the best Ryzen 7 1800X for our scaling trials right out of the gate.
Ryzen 7 1800X : Frequency As A Function Of Temperature At 1.5V
This first experiment explores how the processor behaves at different temperatures with its core voltage fixed at 1.5V. That seems really high for a test at ambient, and we don't want to damage our CPU just for the sake of generating a chart. On the other hand, once the 1800X is at -196°C, a voltage of 1.5V is actually pretty conservative. In the end, we picked this value as the best compromise between risk at ambient and extreme overclocking performance.
At room temperature (20°C), the processor passes a Cinebench R15 run at 4175 MHz. This is a high frequency for Ryzen, achieved at significant risk. Don't try this at home: warm silicon doesn't like aggressive voltage settings.
By lowering the temperature to 0°C, we're able to dial in a 100 MHz frequency increase. So far, we have an improvement of around 5 MHz/°C.
We continue to lower the temperature by pouring liquid nitrogen in the cooling pot until we arrive at -50°C. The frequency gain is now 250 MHz. Our progression remains constant with the same rate of 5 MHz/°C.
Next we see -100°C, giving us an additional 200 MHz. The trend begins to flatten, indicating that the scaling progression is slowing down slightly (4 MHz/°C).
An additional 50°C drop in temperature shows a gain of only 175 MHz at -150°C. The increase is 3.5 MHz/°C.
For the last step, we reach full pot. At -196°C, with a 46°C drop in temperature, the clock rate stabilizes at 5025 MHz (2.7 MHz/°C).
A full pot signifies that our chamber is filled to the brim. We are at the minimum temperature permissible with liquid nitrogen, which is -196°C. To go any lower, you'd need liquid helium: -269 °C.
Thanks uniquely to the reduced temperature, our sample passes Cinebench R15 with an additional 850 MHz overclock. When you hear that these processors love the cold and are damaged by heat, here is the proof.
Ryzen 7 1800X : Frequency As A Function Of Core Voltage At -196 °C
The next experiment tracks our CPU's behavior at various core voltages with a temperature held constant at -196°C. Only the voltage changes; all other parameters remain unchanged.
At 1.5V, we hit the same clock rate seen in the previous set of tests. This makes sense, of course. However, we'll take the time to mention how well our sample scales. In fact, some of the CPUs we tested couldn't hit 4175 MHz even at a core voltage of more than 1.8V.
With an additional 0.1V, the frequency increases 100 MHz. This is significant, but not exceptional. As a reminder, we saw the same gain under air cooling when transitioning from 1.3 to 1.4V, while the shift from 1.0 to 1.1V offered a superior increase of 250 MHz. Before starting these tests, we would have guessed that the clock rate gained by increasing voltage would be amplified at lower temperatures. That's not the case, though.
The same observation applies when we raise the core voltage an additional 0.1V to 1.7V (+100 MHz).
For the next step, we stabilize 75 MHz higher at 1.8V. This frequency is remarkable: 5300 MHz. Such a clock rate is not common with Ryzen.
We halt the trial at 1.85V. Going any higher yields no frequency increase, and the voltage settings start becoming hazardous to our guinea pig.
The progression we just saw cannot be extrapolated to all Ryzen CPUs at the temperatures and voltages we used for testing. Certain specimens will fare worse when cold, some won't accept more than 1.75V, and others will continue scaling beyond 1.9V. This sample is above average though, even if it's always possible to find something better.
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