About Core-M and the MacBook

I was investigating a little bit more about one of the key elements of the MacBookshowcased as part of the Apple Spring Event. I love the industrial design (and Jon Ive's voice, by the way) and the technology deployed in this new laptop. The motherboard is amazingly small, and this is so because Apple has been able to remove the fan system, plus use state of the art technologies.

This was one of the "wow" moments of the presentation. But this is when technology arises to help us to put this in perspective.

First, look at this benchmark results:

These are Geekbench 3 results from a Core-M CPU and an iPhone 6 Plus. Now, imagine how small is the motherboard of the iPhone 6 Plus. Yes, the iPhone 6 Plus is1 GB RAM, and MacBook is an 8 GB RAM system. But storage wise, the iPhone 6 Plus has 128 GB, plus WiFi 802.11ac, cámera, USB/Lightning, audio and even theM7 coprocessor plus the Biometric one.

The real innovation is just here and is the smartphone. CPU ARM architectureimproves at a fastest pace than x86 architecture and the performance of ARM SoCs is getting better with each iteration.

The 5 Watts dilemma

In the MacBook presentation, they claimed that the TDP of the Core-M was just 5 Watts.

But "standard" specs of Broadwell-Y processors are 4.5W. The key point here is to maximize the performance at all costs (1.299$). The Core-M is placed in the lower side of the printed circuit board, probably to be in touch with the aluminium enclosure. This clever topology should be the secret sauce for this extra 0,5W of performance. It seems quite insignificant, but 0,5W out of 4,5W is a 9% extra roomfor MegaHertzs. And 9% is worth the effort when we are running out of performance.

The result is that the Core-M CPU doesn't fit in any spec sheet available in the ARK portal where Intel collects the technical specs of its processors and chipsets.

AnandTech pointed out they were the 5Y70 and 5Y71, but I guess they are the Core-M 5Y31 with the TDP UP frequency set up to 1,1 GHz, the Core-M 5Y51 up to 1,2 GHzand for the fastest one, the Core-M 5Y71 up to 1,3 GHz.

The point is: why Apple didn't choose to usethe official TDP UP parameter and stayed0,1 GHz below for two of the three available CPU options?

You can argue that 0,1 GHz is not big deal. But look at the three available CPU options: they differentiate in steps of 0,1 GHz. And while other manufacturers stick to the Core-M 5Y70 without TDP UP options (and guess a lower price point below the flat 281$ figure) Apple has put a lot of resources tweaking the CPU to get all the extra juice available. And this requires an exponentially increasing amount of design resources to accommodate the thermals of this x86 processors from Intel.

Live test experience

This laptop is, by all means, the pinnacle of laptops. Unfortunately I'm not optimistic about performance neither autonomy. Watts are directly related to performance. And you have to manage just 5 Watts for CPU and graphics. And add the thermal variable to the mix. Keeping the laptop on you lap should be an issue if that interferes with the dissipation of the heat. Not a thermal issue, but a performance one. If the CPU clocks down to keep things cool, the performance will be clocked down as well.

This is just a theoretical analysis, of course. Live experiences are key to fully disclose the behaviour of a system as unique and complex as this MacBook. And to disclose the behaviour of Intel x86 architecture when dealing with low everything: as low as500 MHz clocks and less than 0,7 Volts. 

Architecture convergence

As we saw before, synthetic benchmarks as Geekbench 3 show a similar performance for Core-M and Apple A8 processors. There are differences beyond synthetic benchmarks, of course, but raw performance starts to converge.

ARM and x86 meet in the low power arena. And here is where x86 needs to improve a lot. ARM scales up (apparently) with more dignity than x86 scales down.Intel should be better reinventing x86 with Skylake.