I remember the speculation that lead up to Apple's iPad launch. The list of things everyone expected the device to do was absurd, and the theories on the architecture behind Apple's first branded SoC was just as fantastic. The simplest answer is sometimes the right one and as Ars Technica's Jon Stokes pointed out, the A4 was nothing more than a hardened ARM Cortex A8 core running at 1GHz in the iPad (and 800MHz in the iPhone 4).

The Cortex A8 is something we've covered extensively here so I won't go into great detail right now. It's a dual-issue, in-order architecture with a 13 stage integer pipeline and a non-pipelined FPU.

When Apple announced the iPad 2, it also briefly announced the A5 SoC. The only detail given? The A5 is a dual-core processor with a GPU that's 9x faster than what's in the A4.

There are only two recent ARM architectures that have multicore support: the ARM11 and the ARM Cortex A9. The A8 doesn't come in a multicore variant. Given how many other SoC vendors are shipping dual-core Cortex A9 SoCs, the A5 was likely no different than NVIDIA's Tegra 2, TI's OMAP 4 or Samsung's Exynos in that regard: armed with a pair of Cortex A9s running at 1GHz. Update: Geekbench reports clock speed at 900MHz. Update 2: Apple confirms 1GHz clock speed on the iPad 2 specs page.

Architecture Comparison
  ARM11 ARM Cortex A8 ARM Cortex A9 Qualcomm Scorpion
Issue Width single-issue dual-issue dual-issue dual-issue
Pipeline Depth 8 stages 13 stages 9 stages 13 stages
Out of Order Execution N N Y Partial
FPU Optional VFPv2 (not-pipelined) VFPv3 (not-pipelined) Optional VFPv3-D16 (pipelined) VFPv3 (pipelined)
NEON N/A Y (64-bit wide) Optional MPE (64-bit wide) Y (128-bit wide)
Process Technology 90nm 65nm/45nm 40nm 40nm
Typical Clock Speeds 412MHz 600MHz/1GHz 1GHz 1GHz

The Cortex A9 is similar to the A8 but with an out-of-order execution engine and a shallower pipeline (9 stages). The result is better-than-A8 performance at the same clock speed. The A9 also adds a fully pipelined FPU.

Now it's unclear what the rest of the A5 SoC looks like, but from the CPU standpoint I think it's safe to say that there are a pair of ARM Cortex A9s in there. We can look at the increase in Geekbench Floating Point scores for some proof:

Geekbench 2 - Floating Point Performance
  Apple iPad Apple iPad 2
Overall FP Score 456 915
Mandlebrot (single-threaded) 79.5 Mflops 279.1 Mflops
Mandlebrot (multi-threaded) 79.4 Mflops 554.7 Mflops
Dot Product (single-threaded) 245.7 Mflops 221.7 Mflops
Dot Product (multi-threaded) 247.2 Mflops 436.8 Mflops
LU Decomposition (single-threaded) 54.5 Mflops 205.4 Mflops
LU Decomposition (multi-threaded) 54.8 Mflops 421.6 Mflops
Primality Test (single-threaded) 71.2 Mflops 177.8 Mflops
Primality Test (multi-threaded) 69.3 Mflops 318.1 Mflops
Sharpen Image (single-threaded) 1.51 Mpixels/s 1.68 Mpixels/s
Sharpen Image (multi-threaded) 1.51 Mpixels/s 3.34 Mpixels/s
Blur Image (single-threaded) 760.2 Kpixels/s 665.5 Kpixels/s
Blur Image (multi-threaded) 753.2 Kpixels/s 1.32 Mpixels/s

Single threaded FPU performance is multiples of what we saw with the original iPad. This sort of an improvement in single-core performance is likely due to the pipelined Cortex A9 FPU. Looking at Linpack we see the same sort of huge improvement:

Linpack

Whether this performance advantage matters is another matter entirely. Although there aren't many FP intensive iPad apps available today, moving to the A5 is all about enabling developers - not playing catch up to software.

Memory size, bandwidth and operating frequencies are all unknowns that I was hoping to find out more about once I put hands on the iPad 2. Geekbench reports the iPad 2 at 512MB of memory, double the original iPad's 256MB. Remember that Apple has to deal with lower profit margins than it'd like with the iPad, but it refuses to cut corners on screen quality so something else has to give.

L2 cache size has also apparently increased from 512KB to 1MB. The L2 cache is shared among both cores and 1MB seems to be the sweet spot this generation.

Geekbench 2 - Memory Performance
  Apple iPad Apple iPad 2
Overall Memory Score 644 787
Read Sequential (single-threaded scalar) 340.6 MB/s 334.2 MB/s
Write Sequential (single-threaded scalar) 842.4 MB/s 1.07 GB/s
Stdlib Allocate (single-threaded scalar) 1.74 Mallocs/s 1.86 Mallocs/s
Stdlib Write (single-threaded scalar) 1.20 GB/s 2.30 GB/s
Stdlib Copy (single-threaded scalar) 740.6 MB/s 522.0 MB/s

Geekbench's memory tests show an improvement in effective bandwidth as well. The biggest improvement is in the stdlib write test which shows a near doubling of bandwidth from 1.2GB/s to 2.3GB/s. Unfortunately this isn't enough data to draw conclusions about bus width or DRAM operating frequency. Given the increases in CPU and GPU performance, an increase in memory bandwidth to go along with the two isn't surprising.

Geekbench shows a healthy increase in integer performance, both in single and multithreaded scenarios. The multithreaded advantage makes sense (two are better than one), but the lead in single threaded tests shows the benefit the A9 can deliver thanks to its shorter pipeline and ability to reorder instructions around stalls.

Geekbench 2 - Integer Performance
  Apple iPad Apple iPad 2
Overall FP Score 365 688
Blowfish (single-threaded) 13.9 MB/s 13.2 MB/s
Blowfish (multi-threaded) 14.3 MB/s 26.1 MB/s
Text Compression (single-threaded) 1.23 MB/s 1.50 MB/s
Text Compression (multi-threaded) 1.20 MB/s 2.82 MB/s
Text Decompression (single-threaded) 1.11 MB/s 2.09 MB/s
Text Decompression (multi-threaded) 1.08 MB/s 3.28 MB/s
Image Compress (single-threaded) 3.36 Mpixels/s 3.79 Mpixels/s
Image Compress (multi-threaded) 3.41 Mpixels/s 7.51 Mpixels/s
Image Decompress (single-threaded) 6.02 Mpixels/s 6.68 Mpixels/s
Image Decompress (multi-threaded) 5.98 Mpixels/s 13.1 Mpixels/s
Lua (single-threaded) 172.1 Knodes/s 273.4 Knodes/s
Lua (multi-threaded) 171.9 Knodes/s 542.9 Knodes/s

On average Geekbench shows a 31% increase in single threaded integer performance over the A4 in the original iPad. NVIDIA told me they saw a 20% increase in instructions executed per clock for the A9 vs. A8 and if we remove the one outlier (text decompression) that's about what we see here as well.

Geekbench 2
  Overall Integer FP Memory Stream
Apple iPad 448 365 456 644 325
Apple iPad 2 750 688 915 787 324

The increases in integer performance and memory bandwidth are likely what will have the largest impact on your experience. The fact that we're seeing big gains in single as well as multi-threaded workloads means the performance improvement should be universal across all CPU-bound apps.

What does all of this mean for performance in the real world? The iPad 2 is much faster than its predecessor. Let's start with our trusty javascript benchmarks: SunSpider and BrowserMark.

SunSpider Javascript Benchmark 0.9

Apple improved the Safari JavaScript engine in iOS 4.3, which right off the bat helped the original iPad become more competitive in this test. Even with both pads running iOS 4.3, the iPad 2 is 80% faster than the original iPad here.

The Motorola Xoom we recently reviewed scored a few percent slower than the iPad 2 in SunSpider as well. Running different OSes and browsers, it's difficult to conclude much when comparing the A5 to Tegra 2.

A bug in BrowserMark kept us from running it for the Xoom review but it's since been fixed. Again we're looking at mostly JavaScript performance here. Rightware modeled its benchmark after the JavaScript frameworks and functions used by websites like Facebook, Amazon and Gmail among others. The results are simply one aspect of web browsing performance, but an important one:

Rightware BrowserMark

The move from the A4 in the iPad 1 to the A5 in the iPad 2 boosts scores by 47%. More impressive however is just how much faster the Xoom is here. I suspect this has more to do with Google's software optimizations in the Honeycomb browser than hardware, but let's see how these tablets fare in our web page loading tests.

We debuted an early version of our 2011 web page loading tests in the Xoom review. Two things have changed since then: 1) iOS 4.3 came out, and 2) we changed our timing methods to produce more accurate results. It turns out that Honeycomb's browser was stopping our page load timer sooner than iOS', which resulted in some funny numbers when we got to the 4.3/Honeycomb comparison. To ensure accuracy we went back to timing by hand (each test was repeated at least 5 times and we present an average of the results). We also added two more pages to the test suite (Digg and Facebook).

2011 Page Load Test - Average

The iPad 2 generally loads web pages faster than the Xoom. On average it's a ~20% increase in performance. I wouldn't say that the improvement is necessarily noticeable when surfing most sites, but it's definitely measurable.

The move to iOS 4.3 really narrowed the gap between the original iPad and the Xoom. In some cases the two actually render pages in the same amount of time, however that's typically for lighter pages that are easy to render. Up the complexity and the Xoom easily distances itself from the original iPad.

2011 Page Load Test - AnandTech.com

2011 Page Load Test - Amazon.com

2011 Page Load Test - CNN.com

2011 Page Load Test - Digg.com

2011 Page Load Test - Engadget.com

2011 Page Load Test - Facebook.com

2011 Page Load Test - NYTimes.com

2011 Page Load Test - Reddit.com

We'll touch on this more in the full review but it's not all about performance when talking about web browsing between the iPad 2 and the Xoom. Although the iPad 2 may have faster render times on average, the Xoom still supports tabbed browsing which definitely has its advantages.

Introduction The GPU: PowerVR SGX 543MP2
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  • rom0n - Saturday, March 12, 2011 - link

    The reason why Ipad webloading tests may be better is that it is missing flash. It is not rendering the full web page.
    Unless anandtech is using initial Xoom firmware without flash. The new android 3.0.1 brings Flash 10.2 as well as other performance and stability improvements.
    Reply
  • tipoo - Saturday, March 12, 2011 - link

    I was going to bring that up too. If the Xoom has Flash enabled, its numbers are more impressive. Reply
  • Anand Lal Shimpi - Saturday, March 12, 2011 - link

    The test is run apples-to-apples, there's no Flash enabled :)

    Take care,
    Anand
    Reply
  • VivekGowri - Saturday, March 12, 2011 - link

    Apples to Androids? Reply
  • arthur449 - Saturday, March 12, 2011 - link

    zing! Reply
  • iwod - Saturday, March 12, 2011 - link

    I really hope the A9 is true. Since there are reports they are Dual Core A8. ( Yeah i know ARM doesn't have that basic design ). But if we get A9 now, there is every chance the Apple A6 will be A15 plus Power VR 6. ( The same as Sony Ericsson ) on there next iPhone / iPad.

    But why apple only said 2x CPU Power when clearly Dual Core 1Ghz A9 should be at least 2 - 3 times faster. And test results doesn't always show the IPC improvement in A9.
    Reply
  • winterspan - Saturday, March 12, 2011 - link

    There is no Cortex-A8 multi-core ... Its either a Cortex-A9 or a modified custom-core like Qualcomm's Snapdragon that is a bastard child of A8 and A9 that supports SMP.
    Given the fact that despite the Intrinsity/PA SEMI purchases, the iPad/iPhone ARM chips have all looked like standard Samsung ARM parts, I highly doubt the iPad 2 is running a custom core. It is far more likely it is a standard Cortex-A9, with some custom power IC and other stuff.

    Regarding the benchmarks, there are many other examples where going from Cortex-A8 to dual-core Cortex-A9 doesn't show >100% improvements...
    Reply
  • metafor - Tuesday, March 15, 2011 - link

    Because 2x the cores does not translate to 2x the performance under all but the tiniest fraction of circumstances. Reply
  • tipoo - Wednesday, March 16, 2011 - link

    They were probably being conservative, as very few apps will scale 100% performance wise across both cores. Reply
  • LeTiger - Saturday, March 12, 2011 - link

    "Other hardware chances are the addition of front and rear facing cameras for FaceTime and taking pictures, but unfortunately, they seem to be pieces lifted from the iPod touch and nothing near the iPhone 4's 5 megapixel shooter."

    "chances" might actually trying to be "changes"?

    Just a thought. Thanks again for the write ups lately, It felt ridiculously relieving to get Anand's take on the new mbp and ipad line, I felt like I couldn't trust any other news site's objectivity until I had the scoop with Anandtech :) (and as always, this is the only place I go for legitimate reviews with ACTUAL analysis instead of spec-chimping)

    Keep em' coming!
    Reply

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