Skylake is better but...
Skylake is certainly a better processor than Broadwell, but I really don’t think the mobile version will offer twice the performance of Broadwell laptop, based on all my testing of the desktop parts. There’s a lot more nuance to what defines “speed,” and Skylake offers a lot, especially on mobile. But if you’re being truly honest, and looking at this question core-for-core, Skylake doesn’t boast twice the performance of a Broadwell CPU. That’s like claiming your iPad Pro is faster than 80 percent of portable PCs.
But then there’s the Core i7 model of the Surface Book. What chip is in that? I don’t know. But it’s likely Microsoft is hanging its “two times faster” performance claims on the Core i7 version, which could possibly, conceivably, be a quad-core chip.
It’s not unprecedented, after all. VAIO stuffed a quad-core Haswell CPU into its Surface Pro clone targeted at professionals. You can read about that engineering feat here, where I note that heat, noise and battery life will be a challenge in the VAIO Z Canvas.
If Microsoft chose to put a quad-core Skylake chip in it the Surface Book, it would likely be one of three Intel CPUs that you can peep at here. The problem is all three are rated for 45 watts—which gives them about three times the power and thermal footprint of a dual-core processor. That level of power consumption and heat generation would be pretty hard to pull off in such a thin body.
The next step down is Intel’s newly announced Core i7-6820EQ, which drops power down to 28 watts, but even that wattage is hard to imagine in the Surface Book.
There are a few things that work in Microsoft’s favor, though. Skylake should be a much cooler CPU than the Haswell quad-core in the VAIO Z Canvas. The Intel quad-core chips can also be tuned down to lower frequencies to keep heat under control. But the odds are good that there’s a dual-core Skylake chip in the Surface Book, and not a quad-core chip.
So if it’s a dual-core, could the Surface Book still be twice as fast as the MacBook Pro? Yes and no. It all depends on what you’re testing, and what benchmarks you use.
Discrete graphics for the win
The icing on the Surface Book is the use of an undisclosed Nvidia graphics chip. Microsoft lists it as “8G” and the official press release docs say it has a piddly 1GB of GDDR5 RAM. But in the land of integrated graphics, the 1GB frame buffer and discrete graphics is king. In the thin Ultrabook class, which the Surface Book technically falls into, discrete graphics are typically unheard of these days due to power consumption and thermals. None of the MacBooks have discrete graphics, and neither does the MacBook Pro 13.
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