During our review of the new 17in Macbook Pro we noticed that the chassis became very hot. Further testing shows that the Core i7 CPU is hitting temperatures over 100 Degrees Celsius
Laptop design is largely governed by heat management. There are a few key components inside a laptop that run quite hot. The CPU and GPU are perhaps the most important of these, as they focus huge energy output into a tiny square of silicon. One way that notebook designers have faced this challenge is through the use of metal laptop bodies.
This works to a degree, but the unfortunate side effect is that when things run really hot the entire laptop body heats up to an uncomfortable level., rather than being pleasantly warm in one's lap. Such situations are why product marketers made a concerted effort in the early half of this decade to shift the naming of such devices from laptop to notebook.
Strange testing results
During testing of the latest Core i7-620M based 17in Macbook Pro we noticed that there were problems running certain tests in our benchmark suite. The score being spat out for the Photoshop tests - fourth in a suite of six test applications - in particular was quite low, and we wondered whether it was down to heat issues. When the test was then successfully run as a standalone test with the Macbook sitting on its side, unibody base exposed to the air, we suspected that the Core i7 was struggling within the Aluminium shell of the Macbook.
|We had to resort to running the Macbook Pro on its side in order to complete our benchmark suite for the review.|
To test our suspicions further we booted into Windows (hooray for Boot Camp) and watched what happened when the CPU was loaded to full. Using CPUID Hardware Monitor to show temperatures, we fired up a copy of Dwarf Fortress. This is a single threaded game that uses rudimentary graphics and hardcore algorithms to create a world from scratch. We set Dwarf Fortress up to create a large region with 2500 years of history then sent it to work.
Turning up the heat
This loaded the CPU pretty seriously, and the 50 degree Celsius idle temperature of the Core i7 rocketed up to 84 degrees within the space of minutes. As this happened the Macbook's exterior began to heat as well, starting at the underside near the hinge where the CPU sits, and eventually spreading until the left side of the laptop was uncomfortably warm, and the underside was almost too hot to touch.
We then switched to Maxon's Cinebench 11.5. This is a 3D rendering benchmark that is used to test multithreading in CPUs, and loads up all cores with rendering tasks. During this test the Core i7 spiked at 95 degrees Celsius, tantalisingly close to the boiling point of water. Suffice it to say that the Macbook Pro was attaining temperatures that we wouldn't want anywhere near our laps by this point.
|Our second round of Windows testing. Both the core temps and the CPU diode are showing it running over 100 Degrees.|
We repeated the Cinebench test in OS X, and, as with the Windows version, the CPU temperature climbed precipitously high - topping out at 90 degrees Celsius. The underside heat sensors were only registering 39 degrees when this happened, even though the underside near the CPU was almost too hot to touch.
Round two of testing
To be sure of our results we left the Macbook Pro overnight to cool off. Upon coming back into the office we repeated our tests, first in Windows and then in OS X. By the time the second run of the Cinebench test finished in Windows, the CPU Diode was reporting a temperature of 101 degrees Celsius.
A similar situation occurred in OS X. We've included the graph showing the heat output from the MacBook Pro's sensors below. In it the CPU peaks at 101 degrees, but worryingly the heat buildup in the CPU doesn't register on the enclosure sensors. This is despite the chassis getting hot to the touch, and the heat buildup being registered on all the hardware-based sensors in the Macbook Pro.
|The second round of OS X testing, worryingly the spiralling CPU temperatures dont get detected by the chassis sensors, despite influencing the temperatures of the other hardware sensors onboard.|
To test just how much an influence cramming the Core i7 into the unibody Macbook Pro has we re-ran the tests on a Fujitsu Lifebook SH 760. This uses the same Core i7-620M CPU as the Macbook, but is designed with a copper heatsink that vents out the left side of its plastic shell. The CPU started out with an idle temperature of 40 Degrees. After 3 consecutive Cinebench runs the maximum CPU temperature seen was 81 Degrees, a full 20 below that experienced with the Macbook. It was also cool to the touch.
|Fujitsu's Lifebook SH 760 also uses a Core i7 CPU, yet manages to run it 20 Degrees cooler than the Macbook Pro does.|
Apple sits the Core i7 at the top end of its Macbook Pro Range. From our testing in both Windows and OS X it seems that while the CPU is powerful, the heat output associated with it running at full load is definitely a cause for concern. In this case the fantastic looks of the unibody Aluminium design are let down by the sheer amount of heat buildup experienced.
Cinebench is of course one of the most CPU-heavy tasks we can throw at a system. CPU temperatures of 100 degrees aren't something to expect at every turn, however even our real world benchmarks were pushing CPU temps over 90 degrees.
The generally cool styling of the Macbook Pro just doesn't seem too capable when put up against the sheer output of Intel's Core i7 processor. This is reinforced by the Fujitsu Lifebook running 20 degrees cooler in the same tests with the same CPU.
[Update: A spokesperson from Apple said that the Macbook is "well within the safety requirements set by the US Safety Authority" and that the CPU temperature was "within the settings from Intel" (Specifications for the Core i7-620M provide operating temperatures of 0-105C(min-max)).]
[Update: Just to clarify the comments about the HWMonitor screenshots. The version used (1.15) predates the Core i7-620M CPU's release. This means that HWMonitor incorrectly reports the CPU as a Core i5. The Cinebench program in the background of the shots reports the CPUs correctly as 2.6GHz Core i7-620M models in both laptops. The references to the CPU in the Fujitsu Lifebook are correct.]