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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  • s44 - Thursday, December 06, 2012 - link

    First pixel density is everything, now color calibration... Coincidentally when Apple starts promoting their selling point. Reply
  • zanon - Thursday, December 06, 2012 - link

    None of this is new stuff kid. Pixel density has been something that a lot of us have wanted for a long time, it just somehow never was a priority for anyone. I can easily remember being awed by the IBM T220 (a 22" 3840×2400 [WQUXGA] screen) back in 2001. It used multiple dual link DVI, and the launch price was around $18k, dropping to around $8.5k a year or two later. I hoped back then that it would rapidly proliferate and descend at least to the mere "high end" level, rather then "stratospheric", but it was not to be. Similarly, color has also always mattered for a lot of us. I'm sitting in front of an NEC display built with that in mind, but there has been a whole market of higher end displays and calibration hardware since practically the dawn of color.

    Just because it's only now that, at long last, the industry is moving out of its previous equilibrium doesn't mean there's some conspiracy or "moving targets" or whatever other stupid BS you think of. It would have been nice to see this getting pushed harder and wider literally 10 years ago. Better late then never though. Excellent color and density should be the standard, not the exception, and I'm delighted to see everything suddenly leaping forward again. Density came first, as the most obvious, lowest hanging fruit. Color is next, first with tighter filters, hopefully next year with IGZO and quantum dot films. 120 Hz becoming standard everywhere would be nice too. Whoever helps make that happen gets a hearty thanks from me, even if I never buy any of their stuff directly.
    Reply
  • Sabresiberian - Friday, December 07, 2012 - link

    You are so right here! The introduction of the LCD set us back at least a decade, in terms of color quality, refresh rate, and pixel density.

    I'm not a great fan of Apple the company, but some things they do right, and do better than the PC industry. Displays in portable devices is one of those things. I'm not in the market for anyone's tablet, but I am tempted by the Retina Display notebooks.

    PC portable computer manufacturers take notice: even a somewhat anti-Apple person is considering buying Apple over your junk displays. Time for you to step up your game!
    Reply
  • Arbee - Friday, December 07, 2012 - link

    I would kill for a 20" or 25" 4:3 LCD panel with something like 2048x1536 resolution on a good quality IPS panel with decent color fidelity.

    Heck, at this point I'd like to see any new LCD display that's 4:3 other than what's in the iPad. 4:3 is still preferable for a lot of actual work on computers (programming, word processing, spreadsheets, etc) but the industry decided unilaterally we were all just content consumers and we need a screen optimized only for movies.
    Reply
  • tim851 - Saturday, December 08, 2012 - link

    This is the "logic" of the anti 16:x crowd that I don't get.

    So you would kill for a 25" 4:3 panel with 2048x1536 pixels.

    Why?

    You are aware that a 30" 16:10 panel with 2560x1600px is
    1) physically higher by almost an inch
    2) has 64 more vertical pixels

    Why the dislike for an extra 512 horizontal pixels?

    Also, if you are willing to accept a 20" 4:3 screen: a 27" 2560x1440 screen that sells from 300$ on ebay is also physically higher (by more than 1 inch) and only has 94 viewer vertical pixels (6%)...
    Reply
  • londiste - Saturday, December 08, 2012 - link

    who said anything about dislike for horizontal pixels? it is dislike for lack of vertical pixels.

    anandtech site we're on fits just fine into half of my 1920 horizontal pixels, but the 120 extra vertical pixels that my 1920x1200 screen has over 1080p are extremely useful.
    Reply
  • tim851 - Saturday, December 08, 2012 - link

    The guy I responded to would "kill" for a display with 2048x1536 pixels.

    I wonder why, when he could have bought a display with 2560x1600 years ago.

    That is MORE VERTICAL PIXELS and MORE PHYSICAL SCREEN HEIGHT.

    Also, Anandtech is a very vertical site, I don't see how 120 extra pixels is helping you much there. Is scrolling 10 screens down instead of 9 really bothering you?

    I use Firefox with the tree-style tab addon which puts the tabs in the sidebar, freeing up vertical space and practically using horizontal space. A lot of applications these days are optimized to use horizontal space.
    Had a 21" 4:3 CRT until three years ago and let me tell you I gladly accepted a 16:9 24" LCD.

    I for one prefer using two 'shallow' windows side-by-side instead of once very deep window.
    Reply
  • Olaf van der Spek - Saturday, December 08, 2012 - link

    1600p being 5x as expensive as 1080p is the real problem.

    Yes, more vertical pixels really matter in some cases. It's a bit like running out of memory and having to use swap, it's much slower.
    Reply
  • Arbee - Monday, December 10, 2012 - link

    I don't dislike the extra horizontal pixels, I just want more vertical pixels to go with it. I am a programmer; it is a *substantial* productivity boost to be able to see an entire function on the screen at once. Seeing more width is comparably of very limited benefit.

    And a $300 27" anything is unlikely to have a good-quality panel in it. I am so done with screens that go purple if you don't keep your head perfectly still (that on a $1800 Toshiba laptop) or have a weird tint to them that you can't get rid of.
    Reply
  • xyzzy1 - Wednesday, December 12, 2012 - link

    Much like Digital/CD set back musical reproduction. Digital is still trying exceed what top end analugue playback achieved! Off topic but couold not resist.... Reply

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