The A5X SoC

The ridiculousness of the new iPad begins at its heart: the A5X SoC.

The A5X breaks Apple's longstanding tradition of debuting its next smartphone SoC in the iPad first. I say this with such certainty because the A5X is an absolute beast of an SoC. As it's implemented in the new iPad, the A5X under load consumes more power than an entire iPhone 4S.

In many ways in the A5X is a very conservative design, while in others it's absolutely pushing the limits of what had been previously done in a tablet. Similar to the A5 and A4 before it, the A5X is still built on Samsung's 45nm LP process. Speculation about a shift to 32nm or even a move TSMC was rampant this go around. I'll admit I even expected to see a move to 32nm for this chip, but Apple decided that 45nm was the way to go.

Why choose 45nm over smaller, cooler running options that are on the table today? Process maturity could be one reason. Samsung has yet to ship even its own SoC at 32nm, much less one for Apple. It's quite possible that Samsung's 32nm LP simply wasn't ready/mature enough for the sort of volumes Apple needed for an early 2012 iPad launch. The fact that there was no perceivable slip in the launch timeframe of the new iPad (roughly 12 months after its predecessor) does say something about how early 32nm readiness was communicated to Apple. Although speculation is quite rampant about Apple being upset enough with Samsung to want to leave for TSMC, the relationship on the foundry side appears to be good from a product delivery standpoint.

Another option would be that 32nm was ready but Apple simply opted against using it. Companies arrive at different conclusions as to how aggressive they need to be on the process technology side. For example, ATI/AMD was typically more aggressive on adopting new process technologies while NVIDIA preferred to make the transition once all of the kinks were worked out. It could be that Apple is taking a similar approach. Wafer costs generally go up at the start of a new process node, combine that with lower yields and strict design rules and it's not a guarantee that you'd actually save any money from moving to a new process technology—at least not easily or initially. The associated risk of something going wrong might have been one that Apple wasn't willing to accept.

CPU Specification Comparison
CPU Manufacturing Process Cores Transistor Count Die Size
Apple A5X 45nm 2 ? 163mm2
Apple A5 45nm 2 ? 122mm2
Intel Sandy Bridge 4C 32nm 4 995M 216mm2
Intel Sandy Bridge 2C (GT1) 32nm 2 504M 131mm2
Intel Sandy Bridge 2C (GT2) 32nm 2 624M 149mm2
NVIDIA Tegra 3 40nm 4+1 ? ~80mm2
NVIDIA Tegra 2 40nm 2 ? 49mm2

Whatever the reasoning, the outcome is significant: the A5X is approximately 2x the size of NVIDIA's Tegra 3, and even larger than a dual-core Sandy Bridge desktop CPU. Its floorplan is below:

Courtesy: Chipworks

From the perspective of the CPU, not much has changed with the A5X. Apple continues to use a pair of ARM Cortex A9 cores running at up to 1.0GHz, each with MPE/NEON support and a shared 1MB L2 cache. While it's technically possible for Apple to have ramped up CPU clocks in pursuit of higher performance (A9 designs have scaled up to 1.6GHz on 4x-nm processes), Apple has traditionally been very conservative on CPU clock frequency. Higher clocks require higher voltages (especially on the same process node), which result in an exponential increase in power consumption.

ARM Cortex A9 Based SoC Comparison
  Apple A5X Apple A5 TI OMAP 4 NVIDIA Tegra 3
Manufacturing Process 45nm LP 45nm LP 45nm LP 40nm LPG
Clock Speed Up to 1GHz Up to 1GHz Up to 1GHz Up to 1.5GHz
Core Count 2 2 2 4+1
L1 Cache Size 32KB/32KB 32KB/32KB 32KB/32KB 32KB/32KB
L2 Cache Size 1MB 1MB 1MB 1MB
Memory Interface to the CPU Dual Channel LP-DDR2 Dual Channel LP-DDR2 Dual Channel LP-DDR2 Single Channel LP-DDR2
NEON Support Yes Yes Yes Yes

With no change on the CPU side, CPU performance remains identical to the iPad 2. This means everything from web page loading to non-gaming app interactions are no faster than they were last year:

SunSpider JavaScript Benchmark 0.9.1

Rightware BrowserMark

JavaScript performance remains unchanged, as you can see from both the BrowserMark and SunSpider results above. Despite the CPU clock disadvantage compared to the Tegra 3, Apple does have the advantage of an extremely efficient and optimized software stack in iOS. Safari just went through an update in improving its Javascript engine, which is why we see competitive performance here.

Geekbench has been updated with Android support, so we're able to do some cross platform comparisons here. Geekbench is a suite composed of completely synthetic, low-level tests—many of which can execute entirely out of the CPU's L1/L2 caches.

Geekbench 2
  Apple iPad (3rd gen) ASUS TF Prime Apple iPad 2 Motorola Xyboard 10.1
Integer Score 688 1231 684 883
Blowfish ST 13.2 MB/s 23.3 MB/s 13.2 MB/s 17.6 MB/s
Blowfish MT 26.3 MB/s 60.4 MB/s 26.0 MB/s -
Text Compress ST 1.52 MB/s 1.58 MB/s 1.51 MB/s 1.63 MB/s
Text Compress MT 2.85 MB/s 3.30 MB/s 2.83 MB/s 2.93 MB/s
Text Decompress ST 2.08 MB/s 2.00 MB/s 2.09 MB/s 2.11MB/s
Text Decompress MT 3.20 MB/s 3.09 MB/s 3.27 MB/s 2.78 MB/s
Image Compress ST 4.09 Mpixels/s 5.56 Mpixels/s 4.08 Mpixels/s 5.42 Mpixels/s
Image Compress MT 8.12 Mpixels/s 21.4 Mpixels/s 7.98 Mpixels/s 10.5 Mpixels/s
Image Decompress ST 6.70 Mpixels/s 9.37 Mpixels/s 6.67 Mpixels/s 9.18 Mpixels/s
Image Decompress MT 13.2 Mpixels/s 20.3 Mpixels/s 13.0 Mpixels/s 17.9 Mpixels/s
Lua ST 257.2 Knodes/s 417.9 Knodes/s 257.0 Knodes/s 406.9 Knodes/s
Lua MT 512.3 Knodes/s 1500 Knodes/s 505.6 Knodes/s 810.0 Knodes/s
FP Score 920 2223 915 1514
Mandelbrot ST 279.5 MFLOPS 334.8 MFLOPS 279.0 MFLOPS 328.9 MFLOPS
Mandelbrot MT 557.0 MFLOPS 1290 MFLOPS 550.3 MFLOPS 648.0 MFLOPS
Dot Product ST 221.9 MFLOPS 477.5 MFLOPS 221.5 MFLOPS 455.2 MFLOPS
Dot Product MT 438.9 MFLOPS 1850 MFLOPS 439.4 MFLOPS 907.4 MFLOPS
LU Decomposition ST 217.5 MFLOPS 171.4 MFLOPS 214.6 MFLOPS 177.9 MFLOPS
LU Decomposition MT 434.2 MFLOPS 333.9 MFLOPS 437.4 MFLOPS 354.1 MFLOPS
Primality ST 177.3 MFLOPS 175.6 MFLOPS 178.0 MFLOPS 172.9 MFLOPS
Primality MT 321.5 MFLOPS 273.2 MFLOPS 316.9 MFLOPS 220.7 MFLOPS
Sharpen Image ST 1.68 Mpixels/s 3.87 Mpixels/s 1.68 Mpixels/s 3.86 Mpixels/s
Sharpen Image MT 3.35 Mpixels/s 9.85 Mpixels/s 3.32 Mpixels/s 7.52 Mpixels/s
Blur Image ST 666.0 Kpixels/s 1.62 Kpixels/s 664.8 Kpixels/s 1.58 Kpixels/s
Blur Image MT 1.32 Mpixels/s 6.25 Mpixels/s 1.31 Mpixels/s 3.06 Mpixels/s
Memory Score 821 1079 829 1122
Read Sequential ST 312.0 MB/s 249.0 MB/s 347.1 MB/s 364.1 MB/s
Write Sequential ST 988.6 MB/s 1.33 GB/s 989.6 MB/s 1.32 GB/s
Stdlib Allocate ST 1.95 Mallocs/sec 2.25 Mallocs/sec 1.95 Mallocs/sec 2.2 Mallocs/sec
Stdlib Write 2.90 GB/s 1.82 GB/s 2.90 GB/s 1.97 GB/s
Stdlib Copy 554.6 MB/s 1.82 GB/s 564.5 MB/s 1.91 GB/s
Stream Score 331 288 335 318
Stream Copy 456.4 MB/s 386.1 MB/s 466.6 MB/s 504 MB/s
Stream Scale 380.2 MB/s 351.9 MB/s 371.1 MB/s 478.5 MB/s
Stream Add 608.8 MB/s 446.8 MB/s 654.0 MB/s 420.1 MB/s
Stream Triad 457.7 MB/s 463.7 MB/s 437.1 MB/s 402.8 MB/s

Almost entirely across the board NVIDIA delivers better CPU performance, either as a result of having more cores, having higher clocked cores or due to an inherent low-level Android advantage. Prioritizing GPU performance over a CPU upgrade is nothing new for Apple, and in the case of the A5X Apple could really only have one or the other—the new iPad gets hot enough and draws enough power as it is; Apple didn't need an even more power hungry set of CPU cores to make matters worse.

Despite the stagnation on the CPU side, most users would be hard pressed to call the iPad slow. Apple does a great job of prioritizing responsiveness of the UI thread, and all the entire iOS UI is GPU accelerated, resulting in a very smooth overall experience. There's definitely a need for faster CPUs to enable some more interesting applications and usage models. I suspect Apple will fulfill that need with the A6 in the 4th generation iPad next year. That being said, in most applications I don't believe the iPad feels slow today.

I mention most applications because there are some iOS apps that are already pushing the limits of what's possible today.

iPhoto: A Case Study in Why More CPU Performance is Important

In our section on iPhoto we mentioned just how frustratingly slow the app can be when attempting to use many of its editing tools. In profiling the app it becomes abundantly clear why it's slow. Despite iPhoto being largely visual, it's extremely CPU bound. For whatever reason, simply having iPhoto open is enough to eat up an entire CPU core. 

Use virtually any of the editing tools and you'll see 50—95% utilization of the remaining, unused core. The screenshot below is what I saw during use of the saturation brush:

The problem is not only are the two A9s not fast enough to deal with the needs of iPhoto, but anything that needs to get done in the background while you're using iPhoto is going to suffer as well. This is most obvious when you look at how long it takes for UI elements within iPhoto to respond when you're editing. It's very rare that we see an application behave like this on iOS, even Infinity Blade only uses a single core most of the time, but iPhoto is a real exception.

I have to admit, I owe NVIDIA an apology here. While I still believe that quad-cores are mostly unnecessary for current smartphone/tablet workloads, iPhoto is a very tangible example of where Apple could have benefitted from having four CPU cores on A5X. Even an increase in CPU frequency would have helped. In this case, Apple had much bigger fish to fry: figuring out how to drive all 3.1M pixels on the Retina Display.

Battery Life, Charging & Thermals The GPU & Apple Builds a Quad-Channel Memory Controller


View All Comments

  • PeteH - Tuesday, April 03, 2012 - link

    I have to be honest, after reading through that link I didn't see anything that even implied working conditions had anything to do with the suicides of the factory workers. The only suicide for which there was any real information provided was that of the worker who killed himself after losing the iPhone prototype, and in that case the victim wasn't a factory worker, but someone in logistics.

    Did working conditions have anything to do with the factory worker suicides? Maybe, maybe not. There doesn't appear to be evidence either way.
  • mr_ripley - Wednesday, April 04, 2012 - link

    I posted the Wikipedia link for all the links in the reference section.

    Here's a more direct report:

    And a companion video:

    The video includes an interview of a survivor who is now paralyzed waist down.

    You can choose to patiently read and watch this report or just turn a blind eye like a lot of people do.
  • PeteH - Thursday, April 05, 2012 - link

    I did read the report. It details unbelievably miserable working conditions in the factories, which I don't think anyone is disputing, and concludes that the way to change those conditions is to pressure the electronics companies making the bulk of the profits. None of the above comments dispute any of this. However it does not link working conditions to suicides among factory workers.

    And yet you continue to insist that there is a link, with no evidence to back it up. You make statements like, "over a hundred of them have committed suicide over the working conditions," "...scores of people killing themselves citing poor working conditions," and "there is no disputing the fact that these deaths are related to working conditions," but you provide only conjecture to back it up, no proof. When you do this people start dismissing everything you say out of hand, even the things that are accurate. And worse than that, you run the risk that other people arguing for better working conditions will be tarred with the same brush. Look at what happened to Mike Daisy.

    Again, I'm not saying working conditions didn't contribute to the suicides, I'm saying there is no evidence one way or the other. Until you have evidence (in the form of suicide notes, higher suicide rates among factory workers, etc.) please stop. You may actually be hurting the very movement you're trying to help.
  • mr_ripley - Thursday, April 05, 2012 - link

    Well, I'm sorry if it is inconvenient for you that these individuals have not said it in so many words. Should we expect them to?... Hey, by the way, I know you're going to kill yourself but why don't your write down an explanation first so we can conclusivly say what the reasons are. And even though you are under a lot of stress right now and are clearly not thinking straight SPELL it our for me please...

    Evidence can come in different forms. Not all of it is directly incriminating, in which case the attention turns to the circumstances. So if these reports don't establish a reasonbly clear coorelation to you, then I am sorry but I disagree.

    You can nitpick on specific words in my comments and quible about words such as evidence. But what are you accomplishing here? Are you justifying your own guilt of purchasing a device manufactured here? Are you an Apple or Foxconn mouthpeice? Do they pay your for spreading lies like Foxconn factories are actually a good place to work (which has been said in the previous comments)? Really, it is people like you need to STOP.

    I'm not going to stop saying what I believe is right!! And unlike Mike Daisy I have not fabricated any evidence. At the most, you can complain that I have drawn incorrect conclusions and I am saying the same about you.
  • PeteH - Thursday, April 05, 2012 - link

    It's inconvenient for me that you are lying. You're the one saying that there are, "...scores of people killing themselves citing poor working conditions," not me. Either show me a case where those people who killed themselves cited poor working conditions as the reason, or cease claiming it is fact. You do damage to the movement that's trying to improve things.

    People hear the news reports about Mike Daisy lying to Ira Glass and what they take away is not the specific lies (claiming to witness things had actually happened but that he had only read about), it's that he's a liar and the story wasn't true. They dismiss the whole issue of poor working conditions out of hand. That's what you risk when you lie to get people to listen.
  • mr_ripley - Thursday, April 05, 2012 - link

    Go ahead, nitpick on specific phrases and completely lose the meaning. But the problem is easily corrected. One can argue that citing something does not have to be done on paper as you would in a professional article. To me the workers "cite" the existence of a problem through their actions as words have failed them.

    Still if you want me to rephrase I'll say "scores of people killing themselves in midst of poor working conditions.." Can you prove that this statement is inaccurate??

    And while you ask me for evidence have you ever bothered to see if you can find evidence that these deaths are not related to working conditions. Prove it to me and I'll take back everything I said.
  • PeteH - Thursday, April 05, 2012 - link

    I think you missed the places above where I stated, "I'm not saying working conditions didn't contribute to the suicides, I'm saying there is no evidence one way or the other." That was my whole point. And I did explicitly state that there's no disputing the poor working conditions. So no, I have no problem with your revised statement.

    However, I don't think what I did was nitpicking at all. Nitpicking would be pointing out that a score is 20, so scores would imply at least 40, and I've only seen documentation of 17 suicides (I haven't seen numbers pre-2010). But that's not what I did.
  • shompa - Friday, March 30, 2012 - link

    Manufacturing employees?

    Look at the world! There are about 20 countries in the world that are democratic and have great living standards. Its just 100 years ago since these countries had child workers and harsh condition.

    BTW. My county is on the "top countries" in the world. Still we have the largest suicide rate in our population in the world. Why are you not fighting against the Swedish government that drives thousands to kill them self each year? We live like slaves here with 80% taxes.

    BTW. Do you care if other companies use HonHai/FoxConn or is it just Apple? Are you writing the same thing about Dell/HP and all other companies that use FoxConn?

    What have you done?
    Have you donated money to a chinese worker? Or is Trolling the only thing you manage to do?

  • grave00 - Friday, March 30, 2012 - link

    I was curious about this statement. Could you elaborate. What inconsistency is there?

    "On the iPhone Apple has been entirely too lax about maintaining consistency between suppliers. If it wants to be taken seriously in this space Apple needs to ensure a consistent experience across all of its component vendors."
  • loboracing - Friday, March 30, 2012 - link

    I remember an ad that touted something new to "see and touch". The retina screen is the "see" part but what about the "touch"? Was that just a gimmick meaning you could touch the screen, or is there some sort of different feel to the screen? Reply

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