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More performance and quieter fans with Intel XTU – Undervolting the ThinkPad X1 Carbon 2018 & ThinkPad T480s

Reduced voltage. Intel's new ULV quad-core processors are very fast, but they also get very warm and consume more power, especially compared to the previous dual-core models. We took two current laptops from Lenovo and tried to reduce the core voltage of the processors via the Intel Extreme Tuning Utility (undervolting).

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Basically, every new ultrabook or laptop released since last autumn is equipped with Intel's new 8th Gen ULV-processors. They offer four native CPU cores and are much faster compared to the old dual-cores. However, this also results in higher power consumption and higher temperatures. We have already tested numerous devices and there can be big differences when it comes to the performance utilization. The current ThinkPad lineup alone shows massive differences, as we have seen in this article.

Today, we are going to have a closer look at the processor core voltage with two examples, the Lenovo ThinkPad X1 Carbon (Core i7-8550U) and the ThinkPad T480s (Core i5-8250U). Not every processor is identical, so Intel sets a default voltage to make sure the processor works without problems at the designed specs. This leaves unused potential for optimizations, so you can improve your laptop with some time and testing. We already explained how this undervolting process works in this dedicated article. We used the free tool Intel Extreme Tuning Utility (XTU) for the following examples.

Note: The shown values only apply for our specific test models. Even identical configurations can behave differently and you should be conservative when you try to find the limit. We recommend reducing the voltage in small steps and testing every level with the integrated Intel XTU stress test (see following picture), for example. Notebookcheck assumes no liability for possible damage caused by modifications.

Intel XTU (overview)
Intel XTU (overview)
Intel XTU CPU stress test
Intel XTU CPU stress test

ThinkPad X1 Carbon – Core i7-8550U

The Intel Core i7-8550U in the ThinkPad X1 Carbon can reach up to 3.7 GHz when you stress all four cores, at least in theory. However, this will require much more than the specified TDP of 15 W. Lenovo increases the power limits of the processor to 29 W for short workloads (up to 28 s) and 23 W for longer load periods, which is still sufficient for about 2.9 GHz. The processor runs very hot (over 90 °C) under continuous workloads, which obviously affects the surface temperatures of the slim chassis as well.

We were able to reduce the core voltage (Core Voltage Offset in Intel XTU) of the Core i7-8550U by 110 mV. The processor still hits the TDP limits, so we checked two different scenarios:

First Scenario: Improving the performance

The TDP limits are still in place, so neither the processor temperature nor the power consumption change during our one-hour Cinebench loop. The average core clock on the other hand jumps from ~2.9 GHz to almost 3.2 GHz. This is an 8% improvement in the Cinebench loop, which is not a bad result for a free tuning.

Clock, temperature, and consumption of the processor (standard)
Clock, temperature, and consumption of the processor (standard)
Clock, temperature, and consumption of the processor (undervolted)
Clock, temperature, and consumption of the processor (undervolted)
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Cinebench R15 CPU Multi 64-bit Red: Standard, Yellow: Undervolted

Second Scenario: Reducing temperature and power consumption

You should still optimize the core voltage even if you are happy with the regular CPU performance. We reduced the TDP limits manually (Intel XTU settings Turbo Boost Short Power Max & Turbo Boost Power Max) to get the standard performance, more precisely 22 W for short periods (-> 4x 3.1 GHz) and 17.5 W (-> 4x ~2.9 GHz) for longer workloads for our system. We compared the two Cinebench loops in the diagram below. The processor clock is almost identical, but there are substantial differences in terms of temperature and obviously the consumption (which we set manually). The processor is now 12 °C cooler, which reduces the surface temperatures as well. We could not notice a different fan behavior, though.

Clock, temperature, and consumption of the processor (red: standard, green: undervolted + reduced TDP)
Clock, temperature, and consumption of the processor (red: standard, green: undervolted + reduced TDP)
Cinebench loop top (standard)
Cinebench loop top (standard)
Cinebench loop bottom (standard)
Cinebench loop bottom (standard)
Cinebench loop top (undervolted + reduced TDP)
Cinebench loop top (undervolted + reduced TDP)
Cinebench loop bottom (undervolted + reduced TDP)
Cinebench loop bottom (undervolted + reduced TDP)

ThinkPad T480s – Core i5-8250U

The situation for the ThinkPad T480s is a bit different. The power limit is already set to 44 W, but the Core i5 "only" needs about 29 W for the full 3.4 GHz. The processor maintained its performance level for quite a while during our Cinebench loop, but eventually it had to reduce its performance a bit due to the high processor temperature. The voltage reduction of the Core i5 in the T480s is therefore also supposed to stabilize the performance under sustained workloads, but primarily it should reduce the power consumption and the temperature.

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0102030405060708090100110120130140150160170180190200210220230240250260270280290300310320330340350360370380390400410420430440450460470480490500510520530540550560570580590600610620630640650660670680690700710720Tooltip
Cinebench R15 CPU Multi 64-bit Red: Standard, Yellow: Undervolted

We were able to reduce the core voltage of our Core i5-8250U by 125 mV (Core Voltage Offset Intel Extreme Tuning Utility). The following diagrams show that the CPU now maintains the full 3.4 GHz during the whole Cinebench loop and there are no more fluctuations after 20 iterations. However, the other improvements are much more important, because the average core temperature is almost 15 °C lower and the power consumption is 7.5 W lower! This has a positive effect on the surface temperatures as well, and the battery runtime will also be better in some scenarios. We originally determined a fluctuating noise level of 36.9-38.3 dB(A) during the Cinebench test, but the laptop did not use the highest fan level with the new settings anymore.

Clock, temperature, and consumption of the processor (standard)
Clock, temperature, and consumption of the processor (standard)
Clock, temperature, and consumption of the processor (undervolted)
Clock, temperature, and consumption of the processor (undervolted)
Cinebench loop top (standard)
Cinebench loop top (standard)
Cinebench loop bottom (standard)
Cinebench loop bottom (standard)
Cinebench loop top (undervolted)
Cinebench loop top (undervolted)
Cinebench loop bottom (undervolted)
Cinebench loop bottom (undervolted)

Verdict – Tuning the ULV CPUs with Intel XTU is worthwhile

We have a clear verdict after the test: You should definitely optimize the core voltage of the new Intel quad-core ULVs (8th Gen). The performance improvement is not even the biggest factor here, because the quad-cores are already more than powerful enough for common office tasks. The improvements in the other areas like the temperatures, the power consumption, and sometimes even the fan noise, are much more interesting.

We recommend that every laptop user should optimize the processor core voltage. All you need is free software like Intel's XTU (description and guide available here) and some time to get the maximum out of your device without paying any additional money.

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> Notebook / Laptop Reviews and News > Reviews > More performance and quieter fans with Intel XTU – Undervolting the ThinkPad X1 Carbon 2018 & ThinkPad T480s
Andreas Osthoff, 2018-04-10 (Update: 2018-04-11)
Andreas Osthoff
Andreas Osthoff - Senior Editor Business
I grew up with computers and modern consumer electronics. I am interested in the technology since I had my first computer, a Commodore C64, and started building my own PCs after that. My focus here at Notebookcheck is the business segment including mobile workstations, but I also like to test new mobile devices. It is always a great experience to review and compare new products. My free time is filled with a lot of sports, in the summer mainly on my bike.