Surface Pro 2017

How does the Surface Pro (2017) with Core i5 compare to the Core i7 model, and did Microsoft cut corners to achieve its fanless design? Read on for answers.

Microsoft's Surface Pro for 2017 brings a plethora of slight changes that add up to an outstanding experience. One of those shifts is the new fanless Core i5 model, which is priced to be the better selling of all the models available.

Almost all the professional reviews, including our own, however, featured the high-end and expensive Core i7 version with Iris Plus graphics. How does the Core i5 model compare to the i7 experience for heat, battery life, and performance? I'll put it through a set of tests to discover the answer.

See Surface Pro at Microsoft

Surface Pro Core i5 performance comparison

The Surface Pro comes in two models with the Core i5-7300U. One model has just 128GB of storage and 4GB of RAM ($999) while the second one has 8GB of RAM and 256GB of storage ($1,299) – that second version is what is being reviewed here.

I've already written a deep dive into why this Core i5 is a "true" Core i5 and not a rebranded, low powered Core M or Y-Series chip as many users doubted Microsoft could make such a device fanless without compromise. Of course, the next question is whether Microsoft is intentionally reducing the i5's thermal design power (TDP) from 15W to 7.5W – again to kind of "cheat" by putting in a real Core i5 but making sure it never reaches its full speed and power potential.

Surface Pro's new Core i5 versus Surface Pro 4

Category Surface Pro (2017) Surface Pro 4 i5 Surface Pro 4 i7
Processor 7300U (new) 6300U (old) 6600U (old)
Number of Cores Two Two Two
Number of Threads Four Four Four
TDP 15W 15W 15W
Base Frequency 2.60 GHz 2.40 GHz 2.20 GHz
Max Turbo Frequency 3.50 GHz 3.00 GHz 3.40 GHz
Cache 3MB SmartCache 3MB SmartCache 4MB SmartCache
Graphics Intel HD 620 Intel HD 520 Intel Iris 540

Like all laptops and mobile PCs, there is some degree of power throttling (which is different from CPU thermal throttling) to keep the magnesium chassis of the Surface from getting too hot. Nonetheless, for a passively cooled system, Microsoft's Surface Pro with Core i5 does quite well.

Surface Laptop Core i5 vs. Core i7: Comparing performance and battery life

Before we dive into the thermals, here are raw benchmarks to see how the Core i5 Surface Pro compares to other Surfaces.

Overall, performance with the Surface Pro Core i5 is outstanding and significantly better than the same Surface Pro 4 configuration even without a fan. Those concerned that the fanless Surface Pro is underperforming to stay below thermal limits can be assured that not only is that not the case, but in fact the Pro is faster than the Surface Laptop with a Core i5 configuration.

Surface Pro Core i5 stress test and throttling

The flipside to benchmarks like Geekbench, which has only a short duration, is prolonged duress to the processor to see how heat affects performance. The question of whether Microsoft is purposefully limiting the Core i5 on the fanless Surface Pro is a valid one.

During a stress test using Intel's Extreme Tuning Utility (XTU) app, the Surface Pro with Core i5 processor ran for 30 minutes at 100 percent utilization. The Surface Pro was AC powered and set to "best performance" to ensure maximum processor output. The room temperature was 76 degrees F (24 degrees C) during the test (this matters for reasons explained below).

Surface Pro with Core i5 CPU stress-test using Intel XTU.

The good news is, like in our Surface Laptop tests, there is no evidence of thermal CPU throttling, which is a big concern for many enthusiasts. CPU thermal throttling occurs when the processor hits temperatures that are so high it could damage it. This situation can happen when a manufacturer has improper or inefficient cooling – like perhaps a fanless Core i5 running at 3.5 GHz. CPU thermal throttling can see extreme downshifts in processor speed to cool the processor resulting in a rapidly oscillating performance curve.

There is some throttling occurring, however. Like all laptops and PC tablets, the Surface Pro Core i5 (and i7) will use power limit throttling to keep temperatures in check. Power limit throttling (or PL1) is more about keeping the entire device – specifically the chassis – cool enough to touch and handle, which is necessary for a magnesium tablet. There is a secondary sensor that has a threshold set by Microsoft to ensure the body of the Surface Pro does not burn users (or become uncomfortable to handle).

I noted earlier that the room temperature was 76 degrees F (24 degrees C). Ambient room temperature directly affects power limit throttling since a cold room can help dissipate more heat from the Surface Pro chassis reducing the need for PL1 to take effect. Some enthusiasts even use a USB-powered fan to cool the back of the Surface Pro as this allows the device to run at faster speeds for longer durations. While the overarching results in this article are accurate, there will be variation depending on your exact testing environment.

Surface Pro CPU – Observed traits

Category Core i5-7300U Core i7-7660U
Max TDP observed 18W 21W
Base frequency 2.6 GHz 2.5 GHz
Turbo frequency 3.49 GHz 3.95 GHz
Thermal throttling No No
Power throttling Yes Yes

The results for the fanless Surface Pro with Core i5 are impressive. For one, Microsoft did not reduce or halve the thermal design power (TDP) from 15W to 7.5W, which is something the company could have done to keep the Surface Pro cool. In fact, during peak turbo bursts the Core i5 regularly hit and stayed at the max 3.5 GHz, and it would peak at 18W TDP.

Over a 30-minute stress test of 100 percent CPU usage, however, the Surface Pro's chassis did get warm. As a result, the TDP is reduced to between two and eight watts towards the 30-minute marker. The average processor speed at the end of this stress test was 2.6 GHz, which is the 7300U's base frequency.

Still, even at the 10-minute mark, the CPU was hovering at around 3.1 GHz with a TDP of 11W and 13W. In other words, power limit throttling is an iterative process – the Surface Pro will reduce power to the processor gradually to keep the chassis temperature in check. But even after running for 30 minutes at 100 percent processor usage, the overall speed never fell below the base frequency for the 7300U at 2.6 GHz.

Surface Pro i5 temperature comparison

The Surface Pro (2017) with a Core i5 is a fanless system relying instead on passive cooling – heat just rises out of the radial vent.

Core i7 Surface Pro temperatures after 30 minutes of 100 percent CPU usage.

During the 30-minute stress test, both the Surface Pro with Core i5 and Core i7 were observed for temperatures. As noted earlier, power limit throttling keeps the Surface Pro from getting too hot to touch, and that is seen in the results.

Surface Pro peak temperatures

Category Core i5-7300U Core i7-7660U
Back max temp 108° F / 42° C 112° F / 44° C
Display max temp 111° F / 43° C 113° F / 45° C

While the Core i7 Surface Pro certainly ran warmer than the Core i5 version, it was within only a few degrees, resulting in an overall similar feel.

Core i5 Surface Pro temps after 30-minutes of 100% CPU usage are slightly cooler than Core i7.

Of course, the Core i7 Surface Pro has an active fan to keep it cool, and the fan was certainly audible during the stress test but still significantly quieter than the Surface Pro 3 or Pro 4.

Surface Pro Core i5 battery outlasts i7

Contrary to my Surface Laptop results, there is an observed difference in battery life between the Surface Pro with a Core i5 compared to the Core i7 model favoring the former.

Real-world tests are difficult with modern Intel processors due to the rapid stepping technology that lets the CPU jump from base to turbo and back to base frequency again in milliseconds. Battery life is completely task-dependent with games and rendering programs zapping much more power than running a web browser or using a Windows Store app. Therefore Microsoft (and other companies) use fixed video loop tests to estimate battery life – those tests are consistent and repeatable.

The PCMark Home Battery Accelerated test uses the CPU and GPU together in a looping cadre of tasks like photo editing, video calls, and web browsing until the computer hits around 20 percent remaining battery.

PCMark 8 Home Battery Accelerated

Category Core i5-7300U Core i7-7660U Battery consumption
Time Five hours and six minutes Four hours 81 percent

While that number falls short of Microsoft's claimed 13.5 hours for the Core i5 model remember that a run-down battery test is extreme with non-stop CPU-intensive tasks looping endlessly. Additionally, there is still 20 percent battery left in both devices tackling on a few more hours. Indeed, in my everyday usage between the Core i5 and Core i7 Surface Pros I cannot say that the battery life is that different – they both hit the "roughly eight-hour" mark depending on usage.

Conclusion: Surface Pro with Core i5 is legit

There are a few inferences that can be reached about the fanless Surface Pro with Core i5:

  • Microsoft did not reduce the i5's TDP to achieve a fanless design.
  • The Core i5 model sustains peak turbo 3.5 GHz for short to medium durations (~5 to 15 minutes).
  • Even after 30 minutes of constant CPU usage the processor never dips below 2.6 GHz (base frequency).
  • There is no CPU thermal throttling, but there is power limit throttling, which is expected.
  • Chassis temperature is slightly cooler but similar to the Core i7 model.
  • Battery life appears to be better than the Core i7 model.
  • Surface Pro (2017) Core i5 is significantly faster and gets better battery life than Surface Pro 4 with Core i5.
  • Surface Pro (2017) Core i5 is faster than Surface Laptop with Core i5.

There is some power limit throttling, but as nearly every laptop (and every Surface) uses PL1 to keep the PC from getting too hot.

The important conclusion is that while the Surface Pro cannot maintain running at peak turbo speeds for more than 10-15 minutes, it very gradually tapers down to its base frequency after thirty. You can see this in the Intel XTU graph below – the orange is the CPU speed and while it slightly oscillates it never rapidly drops. That behavior is the same for almost all Ultrabooks that try to balance fan noise with keeping the device cool – even the Surface Laptop does this to a lesser degree. The Surface Pro – both Core i5 and i7 – use power limit throttling more often simply due to the super thin chassis, but there is no significant difference between the Core i5 and i7 Surface Pros.

Surface Pro 2017 full review

For those considering the fanless Surface Pro with Core i5, you don't have anything to fear. Microsoft did not pull any tricks, and the processor does what it is meant to do. Granted, had Microsoft put a fan into the Core i5 it could run at higher processor speeds for more than 15 minutes of 100 percent CPU usage, but for regular consumers running Windows Store apps, photo and video editing, browsing, the Pro with Core i5 behaves like any other PC.

The Core i5 processor is very consistent under extreme CPU duress. While it drops below its turbo the Surface Pro with Core i5 maintains its base CPU frequency.

Obviously, for long gaming sessions in a warm room, or video rendering all Surface Pros will exhibit a winding down of processor speeds to its base frequency, but that is the tradeoff for this form factor versus a 4.5-pound, quad-core laptop.

Overall, I'm quite pleased with the Surface Pro with Core i5 and have no problem recommending it to most people. If you can afford the Core i7 model the performance is better, but the lack of fan with the Core i5 is tempting.

See Surface Pro at Microsoft