Why 8 And 10 CPU Cores In Smartphones Are A Bad Idea – An Auto Industry Lesson

By Patrick Moorhead - May 11, 2015
UPDATED: Headline with new “10 CPU Core SoC” introduced today by MediaTek. As I have written before, the smartphone and mobile SoC industries are headed in a very disturbing direction, one that could mis-direct a lot of R&D, potentially confuse consumers and maybe even become a dis-service to end consumers because companies are developing the wrong solutions. That disturbing trend is the over-marketing of 8 core CPUs in a smartphone, which I call the “8 Core Myth”. What I realized after I wrote the first article was that I may have lost some readers with some of the technical jargon and buzzwords. Therefore, I wanted to come up with an analogy that explained the 8 Core Myth in simpler terms. To do that, I wanted to use an analogy. There are never perfect analogies, but generally speaking, there have been many analogies drawn between phones and automotive platforms. Both platforms fundamentally rely on a central unit (engine/SoC) to provide their power and they are both incredibly complex systems that take many components to deliver the full experience. Both cars and phones are also limited by the amount of energy they can consume either in the form of gasoline or in the form of battery power. The automotive industry had its own “8 Core Myth” and we’re starting to see that industry backtrack from its own race to “more cores” with their race to bigger engines with more cylinders due to fuel economy standards. This happens at the same time that the mobile SoC industry literally goes wild with CPU cores.
Credit: Stephen Bowler, FlickrCredit: Stephen Bowler, Flickr Part of the reason for this backtracking by the auto industry is that in a car, you cannot simply turn off cylinders when you want to in most engine designs and having a bigger engine with more cylinders will ruin your fuel economy. In a smartphone, you can turn off cores when you aren’t using them, but the reality is that in a smartphone you don’t really use more than 3 large cores in any usage given scenario and if you were to use all 8 cores or more, you’d also have horrible economy in terms of battery life. Plus, both engines and SoCs both suffer from thermal issues when you work them to their maximum capability. Engines, however, have exhausts and smartphones do not, which means having an 8 large CPU core processor running all at the cores at the same time will eventually run into thermal issues and must be sparingly used (if ever).
Same size engine, very different results But the automotive industry also gives us some great lessons in extracting vastly more performance out of the same size engine. The Toyota Yaris is a 1.5L four cylinder engine that bangs out 109 horsepower at 6000 rpm. This engine gets fantastic fuel economy but has a top speed of 115 mph and does 0-60 in 10.2 seconds. Now, compare that to the Audi TTS, which also has a four cylinder engine, and you’ll see a pretty vast difference. The Audi TTS 4 cylinder engine manages an impressive 310 horsepower in a 2 liter engine, meaning that Audi is able to extract nearly three times the performance out of their engine with only 30% more engine volume. It also has a top speed of 155 mph and a 0-60 of 4.7 seconds. The Audi, by measure of 0-60 is more than twice as fast as the Yaris.
Car Engine Disp. (L) Cylinders Horsepower 0-60 (s) Top Speed MPG Avg
2016 Toyota Yaris 1.5 4 109 10.2 115 34
2016 Audi TTS 2 4 310 4.7 155 27
The pointless race to more cores
Of course, when there’s talk about performance, there is also a talk about economy and frankly, the average economy of the TTS is 27 MPG, which considering the performance is really quite impressive. The Yaris, on the other hand, has an average economy of 34 MPG, which is more than 20% better than the TTS, but at the sacrifice of being more than 50% slower. But if you had a choice between the two engines, it would be a no-brainer to most people. You would always want the much faster engine with roughly the same, slightly worse, economy. When it comes to mobile SoCs and the CPUs on them, you’ll find that the sweet spot for CPU cores is around 4 large cores, and in most cases you won’t see a SoC using more than 3 at any given moment. While SoC companies continue to race towards more and more CPU cores, some are even rumored to have 10 cores, companies like Apple and Intel have remained steadfast in their choices of CPU cores. Admittedly, on Android, the OEMs and SoC manufacturers have less control of the operating system than Apple, but Apple really is a great example of how using less cores can still give you a great and fast experience. When it comes to Intel, they simply cannot have more than 4 x86 cores if they want to remain power efficient and on a reasonable size die. Apple’s big and fat 64-bit CPU cores are what kicked off the 64-bit SoC race and they still mostly have only dual core SoCs (triple core in A8X for iPads). So, how is it that a dual and triple core implementation is able to deliver a similar or better experience than 8 cores? Because CPU core counts don’t really matter and the quality of your CPUs is what really matters, as well as the other supporting components of the SoC. Do you support the 8 Core Myth? Ultimately, there are many other components of the vehicle that affect the experience, which include the transmission, the suspension and tons of other parts. As in a phone, without a good, well built, engine, there’s very little chance that the other parts, like the GPU, DSP or memory will have a chance to deliver a quality experience. Simply put, the amount of CPU cores don’t matter, the quality of those cores and the other components of the SoC around them is what really matters. If you are in product management, a carrier, in retail, or even a reviewer or benchmarker and support the 8 Core Myth, I ask that you please rethink your stance longer-term on 8 cores. The 8 Core Myth is real and by supporting it, you are potentially mis-directing a lot of industry R&D, potentially confusing consumers and maybe even driving a dis-service to end consumers because your company is solving problems consumers don’t have. Let me know what you think in the comments section. I’ll leave you with this funny Mad TV parody video to ponder the benefits of a 20 blade razor.
Patrick Moorhead
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Patrick founded the firm based on his real-world world technology experiences with the understanding of what he wasn’t getting from analysts and consultants. Ten years later, Patrick is ranked #1 among technology industry analysts in terms of “power” (ARInsights)  in “press citations” (Apollo Research). Moorhead is a contributor at Forbes and frequently appears on CNBC. He is a broad-based analyst covering a wide variety of topics including the cloud, enterprise SaaS, collaboration, client computing, and semiconductors. He has 30 years of experience including 15 years of executive experience at high tech companies (NCR, AT&T, Compaq, now HP, and AMD) leading strategy, product management, product marketing, and corporate marketing, including three industry board appointments.