Synthetic Heat Run And The Impact Of MSI's NOS
In order to really push the GT70 to its limits, you already saw us fully load its Core i7-4930MX CPU and GeForce GTX 780M GPU. Each part is kept at its factory-overclocked frequency, since Xotic PC fully guarantees those settings. The goal was to run the machine until its internal and external temperatures maxed out. The only reason to end a run early would be a hardware failure.
There's a lot going on in this chart. First, turn your attention to the red line, which represents CPU temperature. As the chip gets past that initial 28-second burst of Turbo Boost speed, it quickly spikes to just over 85 degrees Celsius, then quickly falls below 80 as the fan kicks in and the CPU frequency drops to about 3.3 GHz. The temperature stays below 90 degrees for the entire run, showcasing the effectiveness of MSI's cooling implementation, even in the face of Haswell's documented heat issues.
Next, we look at the yellow line illustrating the the battery's charge level. As described earlier, the GT70 employs a "feature" called NOS that draws extra power from the battery if the platform needs more than the AC adapter can provide. At 30%, NOS shuts down and performance is pulled back. Now we see what happens when NOS is disengaged. Looking at the yellow battery line, the discharge rate is even over time until hitting 29% at the 105-minute mark. The transition out of NOS is less dramatic than we expected. The CPU dips down to 800 MHz, then quickly spins back up to about 2.6 GHz. GPU power consumption does not change at all, and the battery charge rate is zero.
When NOS disengages, draw from the walls rises from 179 W to 203. Adding in 10% losses to heat, we'd expect a 180 W power supply to pull 200 W from the wall. We don't understand why MSI doesn't allow its adapter to run at full power all of the time.
The other thing we see when NOS throttles the processor down is the influence of the heat pipe joining the CPU and GPU. Even though the GPU load does not change significantly, the GPU temperature goes down as the CPU generates less heat. MSI's updated thermal solution is now a proven improvement.
The GT70 keeps an overclocked GeForce GTX 780M under 85 degrees for the entire stress test, performing excellently. Intel's chipset does warm up, but stabilizes in the mid-60-degree range. Both storage sensors actually register lower temperatures once the fans kick in, showing excellent separation from other heat sources in the machine, along with commendable overall cooling performance.
The chart below contains another run that we completed with the new BIOS. We had to extend this one to 140 minutes due to improvements in the NOS function.
Temperatures and performance during most of the test remain unchanged with the new BIOS. With the system’s power adaptor now providing 187 W, the battery lasts around 30 minutes longer than the first test. Once NOS disengages and the CPU pulls back to 800 MHz with spikes to 3.2 GHz, the chip's thermals fall off quickly. The effect of the single CPU/GPU heat pipe is even more pronounced since the CPU speed (and therefore, heat) is much lower with the newer BIOS.
Taking a closer look at CPU clock rate during the heat run, we see that the machine enjoys a bit of Turbo Boost acceleration at the beginning, settling around 3.3 GHz once the thermal situation dictates as much. If we weren't also applying a GPU load, the GT70 would likely run at this frequency indefinitely. But because the graphics module is causing battery drain, we also see the impact of NOS disengaging around the 105-minute mark. The dip goes as low as 800 MHz and recovers to 2.6 GHz. Once Prime95 is shut down at 114 minutes, the system jumps back up to 4.1 GHz.
Below is the frequency result for the same run with MSI's newer firmware.
Clock rates remain the same. Once NOS is turned off and the system no longer draws battery power, there's another drop to 800 MHz with quick spikes up to 3.2 GHz. In this situation, the new BIOS does not improve system performance.
The GT70's palm rest and keyboard remained cool throughout testing. The only areas where we felt heat were one corner by the LCD hinge and right above the side exhaust vent. Those spots get warm, but it's still possible to leave your hand there without getting uncomfortable. Plus, those aren't parts of the notebook you'd normally be grabbing. Right-handed users will have no issues with the exhaust heat, though lefties might be more likely to have their mousing hand in front of the side vent.
In the shot above, you can see the GT70's charge rate with NOS disabled and FurMark running. The system is pulling 187 W from the wall, and the battery is being charged at close to 21 W. Below, we see the CPU's power consumption.
If we take the CPU draw of about 16 W and add it to the 21 W being charged, we're able to surmise that about 37 W are available to the CPU when the GPU is fully loaded. A A 37 W Core i7-4702MQ should never have to use NOS to draw power from the system’s battery. A 47 W Core i7-4700MQ, -4800MQ, or -4900MQ is less likely to use NOS, though there are still 10 W that need to be made up somewhere else in the system. With the Core i7-4930MX and GeForce GTX 780M, you have 20 W needed from the battery under full CPU and GPU load. To really get the most out of the GT70 in this power-hungry, overclocked configuration, you really need a larger power adapter, pure and simple.
In order to test how NOS might behave with another CPU, we used Intel's Extreme Tuning Utility to limit the amount of power the CPU is allowed to use. We then played Crysis 3 for 15 minutes and compared the results. At full power, the machine used 4% of its battery in that 15-minute run. Limited to 47 W, the machine used 3%. Limited to 37 W, it consumed 2%. Only at 37 W and a stock GeForce GTX 780M (not overclocked) were we able to get around NOS, still averaging 38 FPS using Very High details at 1920x1080.
Overall, the GT70 performs really well until its battery drops below 30% charge. Because NOS deliberately uses the battery for extra power, expect performance to drop once NOS is disabled. Putting extra wear on a system’s battery during intense plugged-in gaming sessions is not what we would call a desirable feature.
This wear is exacerbated by an AC adapter the delivered less power with MSI's original firmware. With the updated BIOS, battery wear in normal gaming environments is greatly reduced. Titles like Crysis 3 place a taxing load on both the CPU and GPU, compelling NOS to tap into the battery if you're running a high-end Core i7-4930MX and GeForce GTX 780M combination.
We hope MSI continues to optimize its battery situation through additional BIOS updates. We also hope MSI considers bundling a larger power adapter to minimize reliance on NOS. Further, we wish there was a way to completely disable NOS so that you'd have the option to maintain a fully-charged battery.
