CPU Performance

Like the A6, the 4th generation iPad's A6X integrates two custom designed Apple Swift CPU cores that implement the ARMv7 instruction set. The two cores share a 1MB L2 cache, just like they do in the iPhone 5's A6. I spent a lot of time characterizing the architecture and performance of Swift in our iPhone 5 review, so I won't go over a lot of that here. What I will say is that Swift manages to be the best balance of performance and power efficiency in an ARM based CPU core available today. Swift looks a lot like Apple's take on Qualcomm's Krait core. It's not a Cortex A15 competitor from a performance standpoint, but likely a more power efficient design.

Unlike what we saw in the previous iPads, the A6X only boasts a marginal increase in max clock speed (~7%) over the A6. The two Swift cores can run at up to 1.4GHz in the A6X compared to 1.3GHz in the A6.

Apple iPhone/iPad CPU Clock Comparison
  iPhone iPad iPad Frequency Advantage
Apple A4 Generation 800MHz 1.0GHz 25%
Apple A5 Generation 800MHz 1.0GHz 25%
Apple A6 Generation 1.3GHz 1.4GHz 7.7%

CPU performance improves substantially over the 3rd generation iPad thanks to the Swift cores. Unfortunately, big gains in CPU performance aren't always apparent in actual use. The iPhone 5 seemed to subjectively gain more from the move to A6, partially because of just how frequency constrained the A5 in the 4S was. The A5X CPUs in the iPad 3 were already running 25% faster than the A5's CPU cores.

I didn't notice appreciable differences in application launch times, but there are a few areas were the faster CPU cores definitely stand out. Auto enhance in iPhoto completes quicker on the iPad 4 vs. its predecessor. This is especially true for work on large (high MP) images. I don't think a pair of Swift cores is all it takes to make the iPad 4 a suitable photo retouching workstation but it's better than the previous model.

General Use CPU Performance Comparison
  iPad 2/mini iPad 3 iPad 4
iPhoto Auto Enhance 36MP JPG 11.7 seconds 12.0 seconds 9.1 seconds
Batman: The Dark Knight Rises Level Load Time 36.3 seconds 35.9 seconds 31.1 seconds

Scrolling around iOS Maps in 3D view is substantially smoother on the 4th gen iPad compared to its predecessor. We noticed something similar in our comparison of the iPhone 5 and 4S. Web pages do load quicker on the iPad 4, although the differences can be small depending on the complexity of the page in question. The real world responsiveness benefit from the faster CPU cores seems to be in the 10 - 30% range depending on what you're doing. The problem is at the lower end of the scale, it can be difficult to really feel if you're comparing the 3rd and 4th gen iPads.

We're still very limited in good, cross-platform CPU benchmarks. We, once again, turn to JavaScript tests run in the browser. For all of the tablets tested here we're using Chrome for Android and Mobile Safari for iOS.

SunSpider has been a part of all of our mobile performance testing for quite a while now. It's not the perfect benchmark, but the test ends up being a good measure of browser performance as well as cache latency and CPU performance.

SunSpider Javascript Benchmark 0.9.1 - Stock Browser

The Swift cores do an excellent job here thanks to their much improved memory performance. The Nexus 10 should be competitive however the current state of browser optimizations hold it back a bit here.

Google's Octane benchmark is a much larger test than SunSpider, but we're still looking at JavaScript performance. Octane includes all 8 of the tests from Google's older V8 benchmark but adds 5 new ones including a PDF reader, 3D bullet physics engine and portable 3D game console emulator all built in javascript.

Google Octane Benchmark v1

Octane tells a very different story. The iPad 4 does very well, but the Nexus 10's Cortex A15s are really allowed to shine here. The A15 is simply in a different league of performance.

Finally we have Kraken, a seriously heavy javascript benchmark built by Mozilla. Kraken focuses on forward looking applications that are potentially too slow to run in modern browsers today. The result is much longer run times than anything we've seen thus far, and a very CPU heavy benchmark:

Mozilla Kraken Benchmark

We see a similar story with Kraken. Apple improved CPU performance tremendously over the iPad 3, but the Nexus 10 is able to reach new heights.

Why don't we see a direct correlation between these CPU bound js tests and the real world performance numbers I mentioned above? The problem is that most of today's iOS apps are really built for the sort of performance that a pair of Cortex A9s can deliver. I see pockets of CPU bound activity but it's not consistent enough where you're going to necessarily see a dramatic improvement in responsiveness across the board. I do believe the gap is more apparent on the iPhone thanks to the huge difference in frequency between the 4S and 5, but on the iPad the range from subtle to noticeable differences is broader.

Memory Bandwidth

A look at Chipworks' die shot reveals the same memory interface arrangement as we saw in the A5X:


Apple A6X die via Chipworks

The A5X/A6X place the memory interface blocks (and perhaps the controllers themselves?) adjacent to the GPU, while the A5/A6 more tightly integrate the CPU and memory controller. This highlights a pretty substantial difference in priority between the A5/A6 and A5X/A6X SoCs. The latter really do prioritize memory bandwidth delivery to the GPU, and for good reason. The Retina Display equipped iPads have over 4x the number of pixels as the iPhone 5.


iPad 4 DRAM via iFixit

The 4th generation iPad that iFixit took apart had 1GB of Hynix LPDDR2-1066 on-board, which would indicate a small increase in memory bandwidth. Just as we saw with the A5/A5X comparison, the additional memory bandwidth doesn't appear to be available to the CPU cores - only the GPU cores.

Display Analysis GPU Performance
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  • vkn - Friday, December 07, 2012 - link

    I for one appreciate these tests. There is no easy way to judge displays in showrooms. I now have a system of playing the the same hd videos on each device and evaluating subjectively (which sucks) Reply
  • darwinosx - Thursday, December 06, 2012 - link

    You don't know anything. Apple has been doing this on displays for a very long time. Since you are obviously a teenager, probably longer than you have been alive. Reply
  • jabber - Friday, December 07, 2012 - link

    Yes funny that.

    I saw this with NFC.

    Before the finer points of the iPhone5 came out tech journos were all "NFC!!! NFC!!!! ITS THE FUTURE!!!"

    Then the 5 came out with no NFC and it was overnight a switch to "Oh......NFC isn't really all that important! Whats NFC again?"
    Reply
  • name99 - Sunday, December 09, 2012 - link

    Really? Show us RESPECTED tech journalists who were, to use your language "all NFC! NFC! NFC!" about the iPhone5.
    I don't remember Gruber obsessing about this. I don't remember Anand saying this was an essential iPhone5 feature. I don't remember Horace Dediu caring about this.

    Apple has made it quite clear, since they shipped the iPhone 4S, that they view BT4 as a better solution for most of the things that NFC is supposed to do. Given the extreme lack of interesting things being done with NFC, that seems like a good call.

    Your claim is as ignorant as being surprised that the new iMacs shipped without an optical drives.
    Reply
  • Death666Angel - Saturday, December 08, 2012 - link

    Me personally, I don't agree with Anand. The eyes are pretty good at adapting to colors. So unless you have a calibrated PC monitor or something to compare to, you will not notice when colors are off, unless they are off by a big, big margin. I haven't seen a lot of that in the android camp and when it crept up, there were easy fixes by the community. Reply
  • cheinonen - Sunday, December 09, 2012 - link

    Eyes are very adaptable to what is put in front of them, just like ears are with sound over time. That's why all the measures are done by instruments that aren't subject to the adaptability of our vision system. The dE numbers are designed to tell you how visible an error is. With the older 1976 and 1994 formulas, any dE below 3 was thought to be invisible in motion, with < 1 invisible when side-by-side. The dE2000 formula used in these charts is more accurate (in terms of weighing luminance, hue, and saturation errors), but smaller errors are more visible, so a dE of 3 is now worse than a dE of 3 in the old formulas. The dE numbers have a basis in vision science, though, and let you know if an error is visible.

    How well you'll notice, or care, about a color error likely depends on your exposure to correct colors. If you've spent years looking at a calibrated display, then you'll notice the errors almost instantly. If you've never seen one, you won't notice as you have no idea what it should look like. The whole point of calibration is just so when you see something, or design something, everyone else sees it the same way.

    Also, a global fix for color errors isn't likely to work well, as all displays are slightly different and would need to be calibrated individually. You could make some adjustments, but not make them perfectly accurate.
    Reply
  • name99 - Sunday, December 09, 2012 - link

    To add to this point, I am not an obsessive about color. I don't do design work, or know Pantone numbers by heart or anything. But it was obvious enough to me that colors (in particular photos of faces in Contacts) looked different on my mac and my iPhone 1 that I submitted a bug to Apple about it.

    This is, to put it bluntly, the difference between Apple and other people. Other (supposedly technical) people see that a photo of a friend looks slightly different on their phone from their computer --- it's a little too dark or too red or whatever --- and they shrug and say "well, it's always been like that". Apple people say "Why the hell should we put up with this? It's possible to do better." It's this mindset that leads to useful improvements based on actual use cases, as opposed to useless improvements based on spec-boasting.
    Reply
  • Focher - Saturday, December 08, 2012 - link

    Not sure what the problem is. Everything is tested and reported. It's up to you to decide which attribute(s) matter to you.

    If anything, we should really appreciate that AnandTech reviews those attributes. In addition to Apple actually making the display quality a market differentiator for vendors who play in this space, AnandTech deserves credit for ensuring we see which manufacturers are delivering improved display attributes.
    Reply
  • name99 - Sunday, December 09, 2012 - link

    It's silly to claim that Apple has "just started" promoting color calibration.

    Color calibration was added to the original Mac OS in 1993 (ie WAY before OSX) and every year since then Apple has worked to move it a little pervasively into the system as CPU and GPU speed increases have allowed for more on the SW side, and as tighter control of manufacturing have allowed for more on the HW side.
    Reply
  • sprockkets - Thursday, December 06, 2012 - link

    Screw the ipad. We want the Nexus 10 review! Reply

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