The iPhone 6 Review
by Joshua Ho, Brandon Chester, Chris Heinonen & Ryan Smith on September 30, 2014 8:01 AM EST- Posted in
- Smartphones
- Apple
- Mobile
- iPhone 6
A8’s GPU: Imagination Technologies’ PowerVR GX6450
Last but not least on our tour of the A8 SoC is Apple’s GPU of choice, Imagination’s PowerVR GX6450.
When Apple first announced the A8 SoC as part of their iPhone keynote, they told us to expect a nearly 50% increase in graphics performance. Based on that information and on the fact that that Apple was moving to a denser 20nm process, we initially believed that Apple would be upgrading from A7’s 4-core PowerVR design to a 6-core design, especially in light of the higher resolution displays present on the iPhone 6 and iPhone 6 Plus.
Instead our analysis with Chipworks found that only four GPU cores were present on A8, which ruled out the idea of a 6-core design but did narrow down the options considerably. Based on that information and more importantly Apple’s Metal Programming Guide, we have been able to narrow down our options to a single GPU, the PowerVR GX6450.
The GX6450 is the immediate successor to the G6430 first used in the A7 and is based on Imagination’s PowerVR Series6XT architecture. Imagination first announced PowerVR Series6XT to the public at CES 2014, and now just a short eight months later we are seeing the first Series6XT hardware reach retail.
We have already covered the PowerVR Series6/Series6XT architecture in some detail earlier this year so we won’t go through all of it again, but we would encourage anyone who is interested to take a look at our architectural analysis for additional information. Otherwise we will be spending the bulk of our time looking at how GX6450 differs from G6430 and why Apple would choose this specific GPU.
From a technical perspective Series6XT is a direct evolution over the previous Series6, and GX6450 is a direct evolution over G6430 as well. Given a 4-core configuration there are only a limited number of scenarios where GX6450 outright has more hardware than G6430 (e.g. additional ALUs), and instead Series6XT is focused on adding features and improving performance over Series6 through various tweaks and optimizations to the architecture. Series6 at this point is actually over two years old – it was first introduced to the public at CES 2012 – so a lot has happened in the mobile GPU landscape over the past couple of years.
The closest thing to a marquee feature on Series6XT is support for Adaptive Scalable Texture Compression (ASTC), a next-generation texture compression technology that is slowly making its way into GPUs from a number of manufacturers. Designed by the consortium responsible for OpenGL ES, Khronos, ASTC is designed to offer better texture compression (with finer grained quality options) than existing texture compression formats while also being a universal format supported by all GPUs. In Apple’s case they have always been using PowerVR GPUs – and hence all products support PVRTC and more recently PVRTC2 – however ASTC being exposed allows them to take advantage of the quality improvements while also making game development and porting from other platforms easier.
Less visible to users but certainly important to Apple, Series6XT also includes new power management capabilities to reduce power consumption under idle and light workloads. Through finer grained power gating technology that Imagination dubs “PowerGearing G6XT”, GX6450 can now have its shading clusters (USCs) powered down individually, allowing only as many of them as are necessary to be fired up. As Apple continues to min-max their designs, being able to idle at a lower power state can be used to improve battery life and/or increase how often and how long the A8’s GPU uses higher power states, improving overall efficiency.
Apple iPhone GPU Performance Estimate: Over The Years
And, perhaps most importantly overall, Series6XT comprises a series of under-the-hood optimizations to improve overall performance. When it comes to the internals of PowerVR architectures we only have limited details from Imagination on how they operate, so in some areas we know quite a bit about what Imagination has been up to and in other areas their architectures are still something akin to a black box. At any rate Imagination’s goal for Series6XT was to improve performance by up to 50% – this seems to be where Apple’s 50% performance improvement claim comes from – though as we’ll see the performance gains on real world applications are not going to be quite as potent.
What we do know about Series6XT is that Imagination has made some changes to the structure of the USCs themselves. Series6XT still uses a 16-wide SIMD design, but in each pipeline they have added another set of medium/half-precision (FP16) ALUs specifically to improve FP16 performance. Now instead of 2x3 (6) FP16 ALUs, Series6XT bumps that up to 4x2 (8) FP16 ALUs. This is the only outright increase in shader hardware when you compare Series6 to Series6XT, and on paper it improves FP16 performance by 33% at equivalent clock speeds.
The focus on FP16 is interesting, though for iOS it may be misplaced. These half-precision floating point operations are an excellent way to conserve bandwidth and power by not firing up more expensive FP32 ALUs, but the tradeoff is that the numbers they work with aren’t nearly as precise, hence their use has to be carefully planned. In practice what you will find is that while FP16 operations do see some use, they are by no means the predominant type of floating point GPU operation used, so the FP16 increase is a 33% increase only in the cases where performance is being constrained by the GPU’s FP16 performance.
FP32 performance meanwhile remains unchanged. Each USC pipeline contains two such ALUs, for up to four FP32 FLOPS per clock, or to use our typical metric, 128 MADs (Multiply-Adds) per clock.
The rest of Series6XT’s optimizations take place at the front and back ends, where geometry processing and pixel fill take place respectively. Imagination has not told us exactly what they have done here, but both these areas have been targeted to improve sustained polygon rates and pixel fillrate performance. These more generic optimizations stand to be more applicable to general performance, though by how much we cannot say.
One final optimization we want to point out for Series6XT is that Imagination has made some additional under-the-hood changes to improve GPU compute performance. We have not talked about GPU compute on iOS devices thus far, as until now Apple has not exposed any APIs suitable for it (e.g. OpenCL is not available on iOS). With iOS8 Apple is releasing their Metal API, which is robust enough to be used for both graphics and now compute. How developers put this capability to use remains to be seen, but GX6450 should perform even better than G6430.
| Mobile SoC GPU Comparison | ||||||||||
| PowerVR SGX 543MP2 | PowerVR SGX 543MP3 | PowerVR SGX 543MP4 | PowerVR SGX 554MP4 | PowerVR G6430 | PowerVR GX6450 | |||||
| Used In | iPad 2/iPhone 4S | iPhone 5 | iPad 3 | iPad 4 | iPad Air/iPhone 5s | iPhone 6/iPhone 6Plus | ||||
| SIMD Name | USSE2 | USSE2 | USSE2 | USSE2 | USC | USC | ||||
| # of SIMDs | 8 | 12 | 16 | 32 | 4 | 4 | ||||
| MADs per SIMD | 4 | 4 | 4 | 4 | 32 | 32 | ||||
| Total MADs | 32 | 48 | 64 | 128 | 128 | 128 | ||||
| GFLOPS @ 300MHz | 19.2 GFLOPS | 28.8 GFLOPS | 38.4 GFLOPS | 76.8 GFLOPS | 76.8 GFLOPS | 76.8 GFLOPS | ||||
| Pixels/Clock | N/A | N/A | N/A | N/A | 8 | 8 | ||||
| Texels/Clock | N/A | N/A | N/A | N/A | 8 | 8 | ||||
The one wildcard when talking about performance here is going to be clock speeds. Apple doesn’t expose these and they aren’t easy to test for (yet), though in the long term Metal offers some interesting possibilities for nailing that down, or at least getting a better idea of relative clock speeds.
In any case, we’ll take a look at our GPU benchmarks in depth in a bit, but overall GPU performance compared to A7 and its G6430 is consistently better, but the exact performance gain will depend on the test at hand. Some tests will come very close to reaching 50% while others will be just 15-20%. The dependent factor generally seems to be whether the test is ALU-bound or not; because the USC has not changed significantly from G6430 to GX6450 outside of those additional FP16 ALUs, tests that hit the FP32 ALUs in particular show less of an improvement. Otherwise more balanced tests (or at least tests more defined by pixel fillrate performance) can show greater gains. In general we should be looking at a 30-35% performance improvement.
Why Four Cores?
One thing that admittedly surprised us in the revelation that A8 was using a 4-core PowerVR design was that we figured a 6-core design would be a shoe-in for A8, especially since Apple was on the receiving end of the density improvements from TSMC’s 20nm process. But upon further reflection an additional two cores is likely more than Apple needed nor wanted.
The biggest factor here is that coming from G6430 in the A7, performance has seen a solid improvement despite sticking to only four GPU cores. Due to the combination of performance improvements from the Series6XT architecture and any clock speed increases from Apple, A8 gets quite a bit more GPU performance to play with. The increased resolution of the iPhone 6 screen in turn requires more performance if Apple wants to keep native resolution performance from significantly regressing, which GX6450 is capable of delivering on. Never mind the fact that G6430 also drove the iPad Air and its much larger 2048x1536 pixel display.
| PowerVR Series6/6XT "Rogue" | ||||||||||||
| GPU | # of Clusters | # of FP32 Ops per Cluster | Total FP32 Ops | Optimization | ||||||||
| G6200 | 2 | 64 | 128 | Area | ||||||||
| G6230 | 2 | 64 | 128 | Performance | ||||||||
| GX6240 | 2 | 64 | 128 | Area | ||||||||
| GX6250 | 2 | 64 | 128 | Performance | ||||||||
| G6400 | 4 | 64 | 256 | Area | ||||||||
| G6430 | 4 | 64 | 256 | Performance | ||||||||
| GX6450 | 4 | 64 | 256 | Performance | ||||||||
| G6630 | 6 | 64 | 384 | Performance | ||||||||
| GX6650 | 6 | 64 | 384 | Performance | ||||||||
These performance improvements in Series6XT have a cost as well, and that cost is suitably reflected in the estimated die sizes for each GPU. The G6430 was 22.1mm2 on the 28nm A7, while the GX6450 is 19.1mm2 on A8. Though GX6450 is smaller overall, it’s nowhere near the roughly 11.1mm2 a pure and perfect die shrink of G6430 would occupy. Limited area scaling aside, GX6450’s additional functionality and additional performance requires more transistors, and at the end of the day Apple doesn’t see a significantly smaller GPU because of this. In other words, the upgrade from G6430 to GX6450 has delivered much of the performance (and consumed much of the die space) we initially expected to be allocated to a 6-core GPU.
Overall the choice of GX6450 seems to be one of picking the GPU best for a phone, which is an area the G6430 proved effective with A7. As a step below Imagination’s 6-core PowerVR designs, GX6450 delivers a better balance between performance and power than a larger GPU would, which in turn is clearly a benefit to Apple. On the other hand this means A8 is not going to have the GPU performance to compete with the fastest SoCs specifically designed for tablets, though what this could mean for the obligatory iPad update remains to be seen.
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CalaverasGrande - Wednesday, October 1, 2014 - link
there is more than one iphone competitor with no micro SD.That is just a silly argument. But you are just arguing silly specs. Apple has always lagged behind the bleeding edge. Both on computers and IOS devices. They throw a few nice flourishes on top such as retina or touch ID, but the underlying tech has almost always lagged behind the bleed edge. As the author calls out.
dmacfour - Wednesday, October 1, 2014 - link
And it's only bad for people that have some sort of instinctual need to be on the bleeding edge.kidsafe - Thursday, October 2, 2014 - link
Are you done?TruthLoader - Thursday, October 2, 2014 - link
Did you really forget to mention one of Apple's new key features, introduced the first time with this new iPhone iteration, a capability prominently displayed by the newiPhone 6+ and best described by the words of Apple's CEO:
Dear iSheeps,
I am delighted you guys already noticed our brand-new "iBend" feature. We have intentionally kept quiet to preserve the big surprise now unveiled on behalf of our beloved
iSheep. Let me share the following core principles, which were of particular importance throughout the design and development process:
1) Enhance our iSheep's ability to enjoy a panoramic perspective, to be able to make "Panoramas" without moving the iPhone or needing any third party software.
2) We wanted to compete with curved screen models form LG, Motorola and Samsung, mainly offered in their domestic markets.
3) This is our answer to the curved screen displays offered by LG and Samsung, especially the new Samsung Galaxy Note Edge and the LG G Flex:
http://www.theverge.com/2014/9/3/6097297/samsung-g...
http://www.theverge.com/2013/10/27/5036288/lg-g-fl...
4) It is our firm belief and intention to surprise Samsung and LG by showing that we are capable of having an edged display in our phones without actually having one, all for
the purpose of trashing their new curved display phones and offering you a new, well hidden, feature.
5) Last but not the least, we want to sell more replacement screens (remember, screen replacement prices were already provided before our new iPhone launch event took place
(in anticipation of it:), of course that's a feature, feel free to exchange displays now:)).
I am sure some of you iTards might be aware of some articles stating that although our new phones cost about 200$ to 250$ to manufacture (now the old ones cost even less),
http://recode.net/2014/09/23/teardown-shows-apples...
http://news.investors.com/technology-click/092314-...
http://www.techtimes.com/articles/16347/20140926/i...
we are selling them at a huge premium, which means we make a lot of money and I get to enjoy a lot of additional bonifications (indeed, my 15th luxury home has an indoor pool filled
with 100$ bills, hence I'm able to take a bath without suffocating).
More money leads to more attractive innovations like this special iBend (Registered Trademark, Patend Pending) feature you guys will be blessed with, as usual.
Soon we will launch a new iDevice with an additional "S" in its name, it will offer a whole plethora of new features you will be able to make use of, like the possibility to to bend it back and forth to form an S shape. ("iS", Patend Pending)
I sincerely believe you iSheeps are happy with our new iBend 6 Plus, however please let me take the opportunity to thank you all for being such a giant hoard of ignorant,
blind and mindless suckers whose whole purpose in life consists of buying our new iDevice/iCrap (Registered Trademark, Patend Pending) for a very high premium while wasting
their valueless time waiting in the iQueue just to brag about which poor soul enriched me first.
Always remember and never forget, the only thing premium about apple is price, everything else pales in comparison.
We Own you.
Yours Sincerely
Tim Crook.
TruthLoader - Thursday, October 2, 2014 - link
I'm terribly sorry I did forget to correct some typos, nonetheless, here we go (corrected version):Did you really forget to mention one of Apple's new key features, introduced the first time with this new iPhone iteration, a capability prominently displayed by the new
iPhone 6+ and best described by the words of Apple's CEO:
Dear iSheep,
I am delighted you guys already noticed our brand-new "iBend" feature. We have intentionally kept quiet to preserve the big surprise now unveiled on behalf of our beloved
iSheep. Let me share the following core principles, which were of particular importance throughout the design and development process:
1) Enhance our iSheep's ability to enjoy a panoramic perspective, to be able to make "Panoramas" without moving the iPhone or needing any third party software.
2) We wanted to compete with curved screen models form LG, Motorola and Samsung, mainly offered in their domestic markets.
3) This is our answer to the curved screen displays offered by LG and Samsung, especially the new Samsung Galaxy Note Edge and the LG G Flex:
http://www.theverge.com/2014/9/3/6097297/samsung-g...
http://www.theverge.com/2013/10/27/5036288/lg-g-fl...
4) It is our firm belief and intention to surprise Samsung and LG by showing that we are capable of having an edged display in our phones without actually having one, all for
the purpose of trashing their new curved display phones and offering you a new, well hidden, feature.
5) Last but not the least, we want to sell more replacement screens (remember, screen replacement prices were already provided before our new iPhone launch event took place
(in anticipation of it:), of course that's a feature, feel free to exchange displays now:)).
I am sure some of you iTards might be aware of some articles stating that although our new phones cost about 200$ to 250$ to manufacture (now the old ones cost even less),
http://recode.net/2014/09/23/teardown-shows-apples...
http://news.investors.com/technology-click/092314-...
http://www.techtimes.com/articles/16347/20140926/i...
we are selling them at a huge premium, which means we make a lot of money and I get to enjoy a lot of additional bonifications (indeed, my 15th luxury home has an indoor pool filled
with 100$ bills, hence I'm able to take a bath without suffocating).
More money leads to more attractive innovations like this special iBend (Registered Trademark, Patent Pending) feature you guys will be blessed with, as usual.
Soon we will launch a new iDevice with an additional "S" in its name, it will offer a whole plethora of new features you will be able to make use of, like the possibility to to bend it back and forth to form an S shape. ("iS", Patent Pending)
I sincerely believe you iSheep are happy with our new iBend 6 Plus, however please let me take the opportunity to thank you all for being such a giant hoard of ignorant,
blind and mindless suckers whose whole purpose in life consists of buying our new iDevice/iCrap (Registered Trademark, Patent Pending) for a very high premium while wasting
their valueless time waiting in the iQueue just to brag about which poor soul enriched me first.
Always remember and never forget, the only thing premium about apple is price, everything else pales in comparison.
We Own you.
Yours Sincerely
Tim Crook
Kidster3001 - Thursday, October 2, 2014 - link
Wow, just wow. I agree with most of what you say but you are just going to start fights the way you put it all down. You're not helping.BTW, you mention iPhone Galaxy. I agree, the new iPhone resembles recent Galaxy phones very much in physical form. You should take a look at the Galaxy Alpha though. It looks almost identical to an iPhone 5 with the chamfered edges. pretty sad imo.
DudeDoe - Monday, October 13, 2014 - link
Not that everyone else have already call it.... But, plain and simple: No one is forced to buy A or B. If you don´t like it, or don´t have the means, don´t.Respect the decision and opinion of the others.
Or as someone else had pointed: A) The ones that have the means, they truly have the choice, they can either buy it (because they like the style, the tech, or simply because of the ´status factor´), or they can buy a ´dumb phone´ instead (because they don´t care, or don´t have the need).
B) The ones that don´t have the means. Well those don´t have much of a choice and have to live with what is possible... and accept that, and not coming after the others because "he/she can´t have what he/she really want"
Musikus - Monday, October 13, 2014 - link
Lots of words to say lots of lies. How much döes Samsung pay for these lies? Shame on you, you have no honour and no guts!Pandian - Tuesday, October 14, 2014 - link
Apple's hardware division - so well integrated with its software division that we do not distinguish the two as we would with most others - makes a strong profit on its devices. Starting with iPhones, iPads, iPods, etc., their profit margin on the hardware seems beyond reason, yet the plastic phones with equivalent or inferior build make MORE profit.None of these companies can make such quality devices without the WTO allowing slave labour in China, India, African nations, etc.,to compete at level terms with the labour force of the "developed" nations; the same WTO contract that USA, China, UK, Germany, India, Brazil, Australia and other nations from every dimension of the social or economic space signed!
That made the 19 year old, 16 hour/day worker from China/India/rest of Asia/Africa AT PAR with highly educated and qualified workers from Germany, UK, USA, India, China, Western European nations, etc., workers who work in less enslaving conditions! If the iPhone 4,5 & 6 series, as well as the HTC, Samsung and such companies' products, were made in Japan, Germany, USA, UK, France, etc., they will cost more than $9000 to $25000 to make! So, the going prices for the hardware, not just from Apple, but the entire spectrum, is a great deal for the consumer.
Apple's software make huge profit - brain power is tough to quantify!
The people who steal our money most are the service providing "middlemen"! That includes the companies that allow us to USE these toys! The phone plans, the billing of both parties for the same call - minutes are erased from the caller and the receiver in the USA for the same call! Not one PAC has been formed to fight this.
These non-producing middlemen include the telephone, cellphone and the CABLE companies! Add the satellite companies if their plans go thru'.
People drill liquid 1m or 2000m from the surface, refine and sell them for great profits, because the fluid powers ours locomotives. The same companies prevent alternate sources of fuel for the same use! We are so used to it that when the new set of companies do the same, we are numb to the stabs!
I pay $250 to $800 upfront for a device in the USA, and use it as long as possible, years! Much more of my money is taken from me in much smaller installments every month, adding up to $240+ per family per month, just for phones! Cable and broadband adds another $200+ in most households! THAT is a car payment!
While the newer smartphones allow me to do more - play more games, be entertained with video of various forms such as games, stupid cats, etc. (paying more there), enjoy the social behaviour of human collective without being social by just staring into a 4-6 inch screen, the phones are much smaller and better than the first simple cellphones! Their primary function is still to be able to make quality phone calls! And, texts, when important. Their super-smart powers are seen when used at trade (stocks), hospitals, and now 24/7 health monitoring! Same device - simple or complex use, still cheap at the physical level; buy it cheaper with a plan that does not suit you, you are shredding your cash.
So, Apple or Samsung can gouge me for 100% profit on their quality hardware! I am bleeding into a shock state from the "nickel and dime" hemorrhaging of my other services - the phone plans, the contracts, the over the limits, etc.! The cable companies lay down the hardware still poorly to supply broadband, and channel programs that they do not create! There goes my money!
MacDaddy100 - Saturday, October 18, 2014 - link
It's obvious you don't have much experience in technology, you can tell you've been sucked into the Android/ Samsung marketing telling you what you need in a phone.It seems you sold on specs and specs only, It's sad that Android phone have to put such large specs, faster GHZ, More RAM just to keep up with the iPhone, depending on which benchmarks you read, at times the iPhone is faster, at times Android is faster, but overall pretty even, that just shows how inefficient Android is, Needs double the specs to keep up.
You obviously like car analogies, Its like you think a 1000hp Ford Focus will out race a 500hp Porsche 911 on a race track, just cramming horsepower doesn't make it a all-around better.
Its amazing how much Android keeps copying iPhone features every single year, And Android profits keep sinking FAST, just look at Samsung's recent quarter, complete backslide.
Why is Android flagship phones still using 20 year old 32 bit technology?
Its amusing to watch Fandroids brag about their pretty dancing wallpapers, can't you see that Googles precious Green Robot and Samsung marketing machine has you sucked in.