The Apple iPad Review (2012)
by Vivek Gowri & Anand Lal Shimpi on March 28, 2012 3:14 PM ESTThe 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:
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.
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vol7ron - Thursday, March 29, 2012 - link
Think you meant "except" :)adityarjun - Friday, March 30, 2012 - link
No, you aren'tsiddharth7 - Friday, March 30, 2012 - link
Yeah! Kind of a typo :). Also forgot the question mark. :-)Wanted to edit it, but was not able to after posting. :)
Xyraxx - Thursday, March 29, 2012 - link
Ok, gaming clearly the TF came out ahead. Why the backhanded commentary in that section? I don't see that for the sections that the iPad clearly won. TF takes the overall top spot for its gaming performance. But instead of commentary on that, we get aggressive talk about how they should be pushing even further ahead, and how they are failing at it.The controller compatibility is an absolute win for the Android side, but instead of talk about that, we get this "Yeah, but who says controllers will win over touch". Its like every advantage the iPad doesn't win over, gets trotted out and downplayed as if to say it doesn't mean anything, or somehow doesn't matter.
darkcrayon - Thursday, March 29, 2012 - link
Interesting. I got a different impression entirely. It seems like games specifically optimized for the Tegra 3 by nVidia were somewhat better visuallyr, but the iPad has a more extensive game library and considering the GPU is far more powerful than the Tegra 3's, it's only a matter of time before there are far better graphics to be had on iPad games.Though there is no OS level controller support in iOS, both Bluetooth and dock connector controllers are possible (hence the iControlpad iCade, and a few others). It may be that more games support them now on Android, but nothing is stopping developers from supporting them on iOS at this point.
Finally, it's pretty important that ~100% of the iPad games in the App Store will run on the new iPad, which can't be said for the TF as shown in the review, or probably for any other individual Android tablet.
mr_ripley - Thursday, March 29, 2012 - link
It seems to me that the iPad does charge when I plug it into the USB port on my Macbook Pro. In fact I was surprised to see that not only did it not say "not charging" and show the "plugged-in" icon, it also seemed pretty fast (I will have to try it again to see if it was as fast as the power charger).However, when I tried to this morning to plug it into my Lenovo laptop it showed "not charging". Does this only work when plugged into Apple products?
vol7ron - Thursday, March 29, 2012 - link
This question seems better suited for the Apple support forums.doobydoo - Sunday, April 1, 2012 - link
This reply seems better suited to the kids-r-us forum.Aenean144 - Thursday, March 29, 2012 - link
Modern Macs have special USB hubs that output 7 to 8 Watts of power (~5V at ~1.6A). Most Windows machines or non-Macs and older Macs output about 4.5 Watts max. There's a USB battery charging specification, but I'm not aware of any computers that have this implemented.So, most Mac should be able to charge an iPod, iPad, iPhone relatively quickly. A PC with the normal USB specs will typically do it a little bit slower. 40 to 50%. 4.5 Watts is basically the bare minimum. Doable on an iPad 2 with the screen off, but the 2012 iPad will be tough. If you have the screen off, turn off WiFi and Bluetooth, it'll charge ok if Apple lets it. The screen has to be off with 4 Watt power source.
mr_ripley - Thursday, March 29, 2012 - link
Ah ha! Thanks for the clarification. When I saw that I was able to charge my new ipad while using it with my Macbook pro USB, I neglected to bring along my charger to work. Seems like that was unwise.But I still have around 50% power left so should be fine for today. And yes I do use it at work.