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More about the GPU
Remember, we have two Surface Books. One has an Intel dual-core Skylake Core i5-6300U, 8GB of LPDDR3 in dual-channel mode, a 512GB M.2 PCIe SSD drive and integrated graphics only. The other boasts a dual-core Skylake Core i7-6600U, 16GB of LPDDR3, and the Nvidia graphics chip under the keyboard.
It’s the dedicated graphics chip that gets us going. The specific model is unknown—all Microsoft would say publicly is it’s a custom GeForce chip, and Nvidia won’t say squat. Looking at the GPU in our Surface Book, I’m pretty certain it’s a custom version of the GeForce 940m. It has 384 CUDA cores, runs at 945MHz, has 40GBps of memory bandwidth, and features a 64-wide memory bus. That sounds just like the GeForce 940m except for one thing: The chip in the Surface Book has 1GB of GDDR5, instead of the much slower DDR3 of most GeForce 940m laptops.
There were a lot of forum groans when the chip’s details surfaced earlier this week, as some were expecting the GPU to be a higher-performing chip such as the GeForce GTX 950m. Unfortunately the laws of physics don’t allow that today in a 13-inch laptop Ultrabook. If the custom GeForce chip in the Surface Book is indeed a GeForce 940m variant, it likely uses about 25 watts of power. Moving up to the GeForce GTX 950m would double your CUDA cores, memory bandwidth and probably the performance. It would also doubles the power consumption and heat. Today, that class of GPU is limited to larger and heavier laptops—nothing as lithe as the Surface Book.
We know a little more now about the plumbing, too. It’s obviously an internal—umm, external PCIe connection that runs from the Clipboard to the Base unit. The connection is a x4 PCIe Gen 3 that offers about 25 percent the bandwidth of a full x16 PCIe Gen 3 connection. Some will recoil in horror, but it’s plenty and shouldn’t be an issue in the Surface Book.
Thanks to Skylake, both Surface Books performed well in our tests. As you may know, CPU clock speeds ramp up and down based on the load and how hot they get. With Intel’s 5th-generation Broadwell chips, the CPUs would hit their higher Turbo Boost speeds and then, within a few minutes, fall back from, say, 2.9GHz to 2.6GHz. Skylake generally seems to hold much higher clock speeds even under heavy loads, at least on the early machines I’ve tested. Between the higher clock speeds and microarchitecture advances, it adds up to a meaty performance difference.
In our Handbrake Encode test, we transcoded a 30GB 1080p file to the Android Tablet profile. It’s a beefy test that has a CPU running at full load for almost two hours.
Both Surface Books turn in good scores here, but the edge for value goes to the Core i5 Surface Book. The Surface Book with the Core i7 CPU starts off at fairly high speed but settles down to about 2.95GHz for most of the run. The Surface Book with the Core i5 basically sits at 2.85GHz for most of its run. In the end, it’s probably a wash.
One thing you should note: With the CPU sandwiched into a sub-8mm chassis with an LCD panel on top of it, Microsoft doesn’t push the Core i7 in the Surface Book as hard as the Toshiba Radius 12 does. The Surface Book is actually a little slower than the Toshiba Radius 12.
If you’re wondering why the Core i7 Surface Book is slower, you have to think like a manufacturer. How much heat can a PC really handle? How much fan noise are customers willing to tolerate? And what should be the maximum skin temperature of a laptop before users complain? Microsoft favors lower fan noise and skin temps, so it gives up a little performance on very long work loads.
Moving on to Maxon’s Cinebench R15, which measures a PC’s performance in 3D rendering, I compared the same stack of Ultrabooks using various Haswell and Broadwell Core i5, Core i7 and Core M CPUs to again see the Surface Books outpacing the pack. The Core i5-6300U Surface Book even turns in a higher score than the Core i7-5500U in the Lenovo LaVie laptop. In the Surface Books, we see the Core i7 with a clear advantage over its sibling with the Core i5 as Cinebench takes only a few minutes to run.
Core i7 Surface Book is better in sprints
To put a finer point on it, I also ran Cinebench R15 in single-threaded mode. This would simulate CPU performance on most applications which don’t actually use all of the cores. Here I expected to see the Surface Book open space between the Core i5 Surface Book and the Core i7 in the Toshiba Radius 12, and I wasn’t disappointed. This basically tells you if your workloads are shorter and run in bursts, the Core i7 will yield better performance.
Integrated graphics performance
Skylake’s biggest performance benefit is obviously in graphics. All three of the Skylake-based machines in 3DMark Sky Diver show sizeable performance boosts over the Haswell and Broadwell-based devices. Between the Surface Book with the Core i5-6300U and the Dell XPS 13, you’re looking at roughly a 32 percent difference. You may shrug at such an increase because it’s just integrated graphics, but it’s a significant performance upgrade over Broadwell.
But what about discrete graphics and battery performance? Yup, on the next page.
Microsoft Surface Book
Microsoft's Surface Book reboots what you'll think a laptop should be.
- Tremendous battery life
- Beautiful screen
- Doesn't compromise on laptop use and adds wonderful Clipboard mode
- Rather large and heavy
- Very expensive as you add options on
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