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: Apple’s First 20nm SoC
As has been customary for every iPhone launch since the company began publicly naming their SoCs, Apple has once again rolled out a new SoC for their latest line of phones. With the launch of the iPhone 6 series Apple is now up to their eight generation SoC, the appropriately named A8.
After a period of rapid change with the A6 and A7 SoCs – which introduced Apple’s first custom CPU design (Swift) and the first ARMv8 AArch64 design (Cyclone) respectively – A8 is a more structured and straightforward evolution of Apple’s SoC designs. Which is not to say that Apple hasn’t been busy tweaking their designs to extract ever-improved performance and power efficiency, as we’ll see, but our examination of A8 has not uncovered the same kind of radical changes that defined A6 and A7.
The heart and soul of A8 is as always the CPU and GPU. We’ll be taking a look at each of these individually in a moment, but from a high level both of these are evolutions of their predecessors found in A7. Apple’s GPU of choice remains Imagination’s PowerVR, having upgraded from the Series6 based G6430 to Imagination’s newer GX6450 design. Meanwhile Apple continues to develop their own CPUs and A8 packs their latest design, which is an enhanced version of the Cyclone core first introduced in A7.
Stepping away from the GPU and CPU for the moment, the biggest change about A8 is that it’s smaller. As discovered by Chipworks, A8 is being fabricated on TSMC’s new 20nm process, making the iPhone 6 among the first smartphones to be shipped with a 20nm SoC.
This move to 20nm is not unexpected, but nonetheless it is considerable for a couple of reasons. The first is that this means Apple has moved production over to TSMC’s 20nm HKMG Planar process, making this the first time an Apple SoC has been manufactured anywhere but a Samsung fab. There are numerous possible reasons for this – and not every reason needs to be technical – but from a process development standpoint it’s important to note that over the last few generations TSMC has been the leader among contract foundries, being the first to get new processes up and running for volume production.
| Apple A8 vs A7 SoCs | ||||
| Apple A8 (2014) | Apple A7 (2013) | |||
| Manufacturing Process | TSMC 20nm HKMG | Samsung 28nm HKMG | ||
| Die Size | 89mm2 | 102mm2 | ||
| Transistor Count | ~2B | "Over 1B" | ||
| CPU | 2 x Apple Enhanced Cyclone ARMv8 64-bit cores |
2 x Apple Cyclone ARMv8 64-bit cores |
||
| GPU | IMG PowerVR GX6450 | IMG PowerVR G6430 | ||
This move is also quite considerable because it means for the first time Apple is manufacturing their SoCs on a bleeding edge manufacturing process. Prior to this Apple has been slow to utilize new manufacturing processes, only finally utilizing a 28nm process in late 2013 for A7 over a year after 28nm first became available. The fact that we are seeing a 20nm SoC from Apple at a time when almost everyone else is still on 28nm indicates just how much the market has shifted over the last few years, and how Apple’s SoC development is now synchronized with the very edge of semiconductor fabrication technology.
Finally, the switch to 20nm is interesting because after the last couple of generations being so-called “half node” jumps – 45nm to 40nm to 32nm to 28nm – the jump from 28nm to 20nm is a full node jump (note that Apple didn't ever use 40nm, however). This means we are seeing a larger increase in transistor density than in the previous generations, and ideally a larger decrease in power consumption as well.
In practice TSMC’s 20nm process is going to be a mixed bag; it can offer 30% higher speeds, 1.9x the density, or 25% less power consumption than their 28nm process, but not all three at once. In particular power consumption and speeds will be directly opposed, so any use of higher clock speeds will eat into power consumption improvements. This of course gets murkier once we’re comparing TSMC to Samsung, but the principle of clock speed/power tradeoffs remains the same regardless.
Not accounting for minor differences between TSMC and Samsung, in an ideal case Apple is looking at 51% area scaling (the same design on 20nm can be no smaller than 51% of the die area at 28nm). In reality, nothing ever scales perfectly so the density gains will depend on the kind of I/C being laid down (logic, SRAM, etc.). For the complete chip a 60-70% scaling factor is going to be a better approximation, which for Apple means they’ve picked up a lot room to spend on new functionality and reducing their overall die size.
| Apple SoC Evolution | |||||
| CPU Perf | GPU Perf | Die Size | Transistors | Process | |
| A5 | ~13x | ~20x | 122m2 | <1B | 45nm |
| A6 | ~26x | ~34x | 97mm2 | <1B | 32nm |
| A7 | 40x | 56x | 102mm2 | >1B | 28nm |
| A8 | 50x | 84x | 89mm2 | ~2B | 20nm |
Meanwhile once again this year Apple opened up on die size and transistor counts. A8 weighs in at around 2 billion transistors, as opposed to the “over 1 billion” transistors found on A7. We also have the die size for A8 – 89mm2 – which is some 13% smaller than A7’s 102mm2 die. This makes it clear that Apple has chosen to split their transistor density improvements between adding features/performance and reducing their size, rather than going all-in on either direction.
In the case of using a bleeding edge node this is generally a good call, as Apple and TSMC will need to deal with the fact that chip yields at 20nm will not be as good as they are on the highly mature 28nm process. With lower chip yields, a smaller die will offset some of those yield losses by reducing the number of manufacturing flaws any given die touches, improving the overall yield.
A8 With POP RAM Removed
Moving on, looking at A8 we can see that Apple’s memory subsystem design has not significantly changed from A7. Once again Apple has placed an SRAM cache on the chip to service both the CPU and the GPU. Based on an examination of the die and of latency numbers, this L3 SRAM cache remains unchanged from A7 at 4MB. Meanwhile we also find a series of SDRAM interfaces which drive the A8’s package-on-package (POP) based main memory. Based on teardowns from iFixit, Apple is using 1GB of LPDDR3-1600, the same speed grade of LPDDR3 and capacity that they used for the iPhone 5s. iFixit has found both Hynix and Elpida memory in their phones, so Apple is once again using multiple sources for their RAM.
When we start poking at memory bandwidth we find that memory bandwidths are consistently higher than on A7, but only ever so slightly. This points to Apple having worked out further optimizations to make better use of the memory bandwidth they have available, since as we’ve previously determined they’re still using LPDDR3-1600 speeds.
| Geekbench 3 Memory Bandwidth Comparison (1 thread) | ||||||
| Stream Copy | Stream Scale | Stream Add | Stream Triad | |||
| Apple A8 1.4GHz | 9.08 GB/s | 5.37 GB/s | 5.76 GB/s | 5.78 GB/s | ||
| Apple A7 1.3GHz | 8.34 GB/s | 5.21 GB/s | 5.67 GB/s | 5.69 GB/s | ||
| A8 Advantage | 9% | 3% | 2% | 2% | ||
The Stream Copy score ends up being the biggest gain at 9%. Otherwise the rest of the benchmarks only show 2-3% memory bandwidth increases.
More interesting is memory latency, which shows some unexpected improvements once we get out of the L1 and L2 caches. At both the 1MB – 4MB region of the SRAM and 6MB+ region of main memory, memory latency is consistently lower on A8 versus A7. In both cases we’re looking at latencies about 20ns faster than A7. This identical 20ns gain tells us that that Apple is still doing main memory lookups after the L3 lookup fails, and this in turn means the 20ns gain we’re seeing is due to L3 cache optimizations. We have a couple of ideas for how Apple could have improved L3 latency by nearly 20% like this, but at this time with Apple staying quiet on their architecture like usual, it’s not apparent which of these ideas are the correct ones.
Turning our eyes back to A8 one final time, we find that while a lot of die space is occupied by the CPU, GPU, and SRAM (as we’d expect), there is also quite a bit of space occupied by other blocks Apple has integrated into their design. Without already knowing what you’re looking for these blocks are difficult to identify, but even without being able to do this we have a reasonable idea of what blocks Apple has integrated. Among these we’ll find audio controllers, USB controllers, video encoders/decoders, flash memory controllers, the camera ISP, and of course all kinds of interconnect.
All of these blocks are fixed function hardware (or at best, limited flexibility DSPs), which are equally important to not only the A8’s functionality but power efficiency. By assigning tasks to dedicated hardware Apple does spend some die space on that hardware, but in return these blocks are more efficient than doing those tasks entirely in software. Hence Apple (and SoC designers in general) have a strong incentive to offload as much work as possible to keep power consumption in check. This move towards more fixed function hardware is part of a general “wheel of reincarnation” cycle that has been a constant in processor design over the years, which sees a continuous shift between fixed function and programmable hardware. SoCs, for the most part, are still going towards fixed function hardware, and this should continue for a while yet.
In any case, while we can’t identify individual blocks on A8 we do know that Apple has added a few features to A8 that are present in some form or another among these blocks. New to A8 is some mix of H.265 (HEVC) hardware, which would be necessary to enable the FaceTime over H.265 functionality that is being introduced on the iPhone 6. Apple’s “desktop class scaler” that is used for handling non-native resolution applications and for down-sampling the internal rendering resolution of the iPhone 6 Plus would also be present here.
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Samus - Tuesday, September 30, 2014 - link
tl/drAceMcLoud - Tuesday, September 30, 2014 - link
lol, retardroids crack me upninjaroll - Tuesday, September 30, 2014 - link
LOL. That's pretty sad. I would NEVER spend more than 2 minutes writing about a product I don't intend on using. You seem a LITTLE obsessed with Apple judging by your username. But I applaud you for having so much free time, must be nice having so much disposable time. I say you focus on using whatever works for you.bigstrudel - Tuesday, September 30, 2014 - link
It took a second to scroll by your post, but I had to scroll back up to read your line"Last but not least, every Apple product includes a direct hotlink to the NSA, free of charge, something that might make it a good value, after all."
Wait. Apple is the one with NSA connections?
Aljazeera released emails that show Google's founders speaking with the NSA director on a first name basis.
In 2004, Google bought Keyhole, a geospatial data visualization company with history and investments made by the CIA. Keyhole's marquee application suite, Earth Viewer, emerged as Google Earth in 2005 while other aspects of its technology were integrated into Google Maps.
SELinux was created by the NSA for "security purposes" and is included on Android with Google's permission. It cannot be disabled.
Do you think AOSP will save you with it's "millions of eyes" strategy? Wrong. Google Apps are closed source and cannot be removed by 99% of the population.
Yes. We don't really know what happens to the data that Apple collects. But Apple is a hardware company. They make their money selling devices.
We do know what Google does with our data however. Google exists to collect and sell user data. Distributing an OS and App package that collects user data is a far better strategy for mass spying than trying to directly compete with only a single companies hardware.
And there is nothing to stop Google from handing over anything they want behind closed doors, like you accuse Apple of, but with no evidence.
WinterCharm - Tuesday, September 30, 2014 - link
Someone's upset that their phone isn't the "best"bigstrudel - Tuesday, September 30, 2014 - link
DEVS.2nd response with a wall of text? On a popular website? Impossible. He clearly had it pre-prepared before the review was even ready seeing as it's the size and quality of a 7th graders essay.
Delete this trash.
RandomReader - Thursday, October 2, 2014 - link
You never stop making censorship requests, do you?Here we go again:
In contrast to you I very much enjoyed reading the differing viewpoint mentioned above, albeit the fact that it does display a healthy dislike for apple products in general and has been written by an obvious android fan-boy.
Now what I don't like that much is your request to censor the aforementioned post and all related answers out of purely private motives.
Just because you deem something inappropriate and dispensable, it doesn't has to be that way, thus I politely ask you to respect the right of others to enjoy unhindered freedom of speech in general and the existence of other peoples personal opinions.
Hereby I politely ask you to abstain from censorship requests out of mainly egoistic, egocentric motivations, please respect other peoples rights and opinions.
As a side note, based on your behavior and the totalitarian nature of your requests, I suspect you to be either a member of some law enforcement entity or
an individual blessed with a pretty weak character, apparently unable to deal with differing viewpoints in a grown up, factual manner.
kattahn - Tuesday, September 30, 2014 - link
"The apple way, selling over expensive crap to stupid consumers that like toget robbed."
starting at 200$ is the price that every companies top end smartphone starts at. iPhones have always been priced competitively.
"The iwatch is such an ugly piece of crap" - opinion
"Some characteristics are glaringly obvious and inherent to it: over expensive" - compared to what
"hardly innovative" - combining messaging, navigation, and health features into a watch with TONs of interchangeable bands, integrating the watch dial as manual control, and the ability to use touch feedback to the user to communicate non-visual messages. Inductive charging without the need for a cradle. Theres really no other smart watch doing all of this...
"limited functionality and usability (need of an iPhone to make it work)" - Yup. Its an extension of your phone. this is normal.
"looks exactly like a toy watch and so on." - Have you seen it with any of the nice metal bands? And with the face up? What kind of toy watches are you looking at?
"There are of course way better smart watches out there, especially from the
likes of Samsung, Sony, Motorola, Asus, LG, simply put, there is no need for
another piece of over expensive junk." - You've never used a wearable before, have you? Or read any reviews? Every android one so far has been pretty terrible, with the "flagship" that everyone was waiting on using a 4 year old SoC.
"The iPhone 6 is technologically stuck in pre-2011 times, a base model with
a capacity of 16GB without the possibility to use SD cards isn't even funny
anymore. " - I 100% agree. Apple is making a ton of money off limiting storage capacity.
"Now the Iphone 6 Plus offers a „Retina HD“ screen, full 1920x1080p, oh wow,
where have you been for the past 4 years apple, talk about trailing behind." - First 1080p smartphones came out in q4 of 2012.
"Car engines come to mind. For comparisons shake let’s look at a 1.0 liter, turbo
charged petrol engine and a V8 compressor. What’s better should be obvious, but
by calling the former an „ecobooster“, thus giving it a special marketing label,
this joke becomes a „feature“, something positive that can be added tot the list
of features of a car." - so we've made it clear you know literally cars. got it. stick to analogies with things that you understand.
"FACT: Apple has been forced to copy Android in style and size for
years because people abandoned their tired, moribund and fossilized
devices for superior and innovative Android devices." - Yes, they'e been taking the best features of android for a while now, and leaving the bad ones behind. And they've got a damn fine product to show for it.
"charge a premium price and
wait for the rubes like Jim Smith to hand over their cash like the good
iSheep they are." - Again, iphones are priced the same as any other smartphone.
"For all their squealing about Retina displays, they never even had a HD display until now;
8th time is the charm, though you need the iPhone Galaxy Note to get the 1080p that many Android
users have had for at least a year and is now considered
bare-minimum spec." Yes, androids have been pushing resolutions WAY higher than their processors and batteries could handle for several years. And they've been laggy/stuttery and have had terrible battery life the whole time.
And thats the part that you and the other fanboys just don't understand. Specsheets are boderline useless. Ask intel about spec sheet races during the netburst era of CPUs. Intel ran out clock speed improvements like crazy and got trounced with better user experience and performance by AMD CPUs running half the clock rate.
We can also use your inept car analogy here. Because with engines, bigger is not always better. Not by a longshot. A BMW M3 with a twin-turbo straight 6 pushes more HP and will outperform a Mustang with a 5.0L V8. An Ariel Atom with a 2.3L naturally aspirated engine will beat both cars in 0-60, and will outhandle them both. Because the entire car was built around performance. Point being, If all you look at is horsepower or engine size, you have no idea what you're doing and aren't really getting the best product for what you're trying to do.
Apple creates fantastic, tightly designed products that focus on the user experience. They have 100% control of their hardware and software ecosystems and are able to highly optimize everything they do to provide the highest level of performance they can. If you pick up an iphone 6, regardless of the specs, the screen will look great, the battery life will be great, the phone will be flawlessly snappy and won't lockup/hang/get slow over time. You'll have a great user experience, even if it doesn't spec for spec line up against a 2014 android flagship. Just like if you get into an ariel atom and hit the gas, it will absolutely throw you back against the seat and show you power and acceleration you've never felt before, even though by specs it doesn't look comparable at all to something like an M3 or a Mustang 5.0
Ant1matt3r - Tuesday, September 30, 2014 - link
I've never seen so much admiration or hatred for a company as I have Apple. Have you thought to think that, considering the length of your diatribe, that Apple is doing something RIGHT?I mean, to polarize the world into groups of fanbois and haters, with each being equally passionate about Apple, I'd have to say that they're doing a damn fine job.
If they can compel you to write a 5,000 word essay denouncing their product, imagine what they do for people who actually ENJOY what they do.
dmacfour - Wednesday, October 1, 2014 - link
I don't think the world is actually polarized.There's the 5% that are Apple fanboys, the 5% that would murder Steve Jobs if they had the opportunity, and then the 90% that'll buy wherever is the coolest.One thing is certain: the iPhone is a superior product from a business standpoint.