The Right SoC at the Right Time: Apple's A5

Here's how I know Apple is masterful at marketing. After first showing off the new iPad Apple had tons of press convinced that the company was no longer competing based on specs but rather only interested in delivering an experience. In reality Apple is competing with hardware even more than before, it's just trying to give the public the impression that it's not. After all, Apple doesn't make the vast majority of the technology inside the iPad but it does control the experience. A competitor may be able to ship a dual core Cortex A9 but it can't ship the iOS experience. Is it really a surprise that Apple would downplay what it doesn't have exclusive rights to and instead try to get everyone to focus on what it does? Make no mistake, Apple is very much playing the specs game - in fact it's playing the game harder than anyone else in the industry today.

At the heart of the iPad 2 is a brand new SoC: the Apple A5. Built on what I assume is Samsung's 45nm process the A5 is a much more powerful SoC than it's predecessor the A4.

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

While the A4 featured a single core ARM Cortex A8, the A5 integrates two ARM Cortex A9s with a total of a 1MB L2 cache. That puts the A5 at a similar level of CPU performance to NVIDIA's Tegra 2 and TI's OMAP 4430. The only insider information I've managed to come across points to A5 featuring ARM's MPE (SIMD/NEON engine) in its A9 cores.

Based on Chipworks' analysis of the Apple A5 die it looks like Apple implemented a dual-channel LP-DDR2 memory controller, similar to TI's OMAP 4430.

ARM Cortex A9 Based SoC Comparison
  Apple A5 TI OMAP 4 NVIDIA Tegra 2
Clock Speed Up to 1GHz Up to 1GHz Up to 1GHz
Core Count 2 2 2
L1 Cache Size 32KB/32KB 32KB/32KB 32KB/32KB
L2 Cache Size 1MB 1MB 1MB
Memory Interface Dual Channel LP-DDR2 (?) Dual Channel LP-DDR2 Single Channel LP-DDR2
NEON Support Yes (?) Yes No

Had it not been for NVIDIA Apple would've had the first shipping dual-core Cortex A9 SoC on the market. This is ultimately why Apple is producing it's own SoCs - most of the players in the SoC space don't seem to be moving fast enough for Apple's hardware schedule. Given the aggressive yearly product cadence I wouldn't be too surprised to see a dual-core Cortex A15 in the Apple A6 a year from now. Remember that much of Apple's success has come from being able to control it's hardware and software development. On the Mac side Apple has an extremely aggressive chip partner with Intel, but with the iDevices there is no equivalent (for now). Until that changes, Apple will continue to produce it's own SoCs. It's not that Apple is designing any of the IP that goes into the SoC, it's that Apple is piecing together what it needs, when it needs it.

We've already gone through the performance offered by the A5 over the A4, but to quickly recap: it's a huge increase. While the original iPad felt slow, the new one feels much faster. I would be lying if I said it was fast enough, but it's way better than the original.

CPU Performance

Taken from our iPad 2 Performance Preview:

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.

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.

Double the Memory, Still Not Enough

On a Mac or PC if you don't have enough system memory and go to run a new application you'll get a lot of swapping to disk. The OS will write least recently used pages of memory to disk and evict them from main memory, making room for the newly launched application. Memory management in iOS works differently. All applications are required to save their state as soon as they move from the foreground as iOS can evict them from memory at any point in time.

Having more memory in iOS means you can have apps with larger memory footprints or you can keep more apps in memory without forcefully evicting them, but it generally doesn't mean you'll see improved performance.

With the iPad 2 Apple chose to only equip the device with 512MB of LP-DDR2 memory. That's half of what you get in the Motorola Xoom, but twice what you got in the original iPad. This does mean that (as we mentioned earlier) things like web pages can remain in memory longer, although there's no real impact on performance from what we can tell.

If Apple follows its short tradition, we may see more memory in the iPhone 5 and then more in the iPad 3 next year. Display resolution didn't increase so there's no pressure for additional memory there, but Apple is definitely holding developers back by not throwing even more hardware resources at the iPad 2.

Industrial Design & The Future The GPU: Apple's Gift to Game Developers
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  • jalexoid - Saturday, March 19, 2011 - link

    The movie editing app on Honeycomb is there. And it's similar to iMovie.
    The Office look alike apps on iPad are still not good.

    Honeycomb struggles on the apps side, because the developer hardware was not there, when it was needed.
    But saying "So far only iOS has the most real apps" is a bit incorrect.
    Reply
  • WaltFrench - Sunday, March 20, 2011 - link

    “The movie editing app on Honeycomb is … similar to iMovie.”

    Yes, except for one thing: the YouTube of it shows it unable to show thumbnails properly and balky, rough animations. This wouldn't even get bronze at a beer-fueled coding contest.

    The two are exactly as similar as night and day: they live on the same planet.
    Reply
  • Zoomer - Saturday, March 19, 2011 - link

    >>Also, when you take it out in front of a client during a lunch meeting, it tends to impress them.

    That's probably why most buy it.
    Reply
  • Azethoth - Sunday, March 20, 2011 - link

    I bought my iPad to turn my daily NY Times habit at Starbucks paperless. So Wi-Fi only and one year = it paid for itself.

    Acting as an awesome controller for my home stereo setup is a total bonus. Same with reading books again via iBooks and Kindle.

    Yes, the underlying thing is I use it to consume and not to create. Unless you find an application that uses its strength in that regard it will just frustrate you as you try to do your pad-inappropriate netbook / laptop / PC / mini / mainframe or whatever apps on it.

    For me its a perfect way to avoid the netbooks / laptops which I have always loathed but get a little mobility. But then I only create on a desktop with 2560 x 1600 resolution so laptops will never cut it anyway.
    Reply
  • synaesthetic - Sunday, March 20, 2011 - link

    It's pretty refreshing to see someone who has actually found a usable niche for these things.

    It's just not too useful to a lot of folks. I carry my laptop to class already--yeah, this big, heavy MSI gaming laptop--because I need it. If I could carry something as light as the iPad and have it do what I need... I'd be sold.

    But it can't. And LCDs suck for long reading sessions. I'd rather have an ereader.
    Reply
  • doobydoo - Sunday, March 20, 2011 - link

    what is it you can't do on an ipad? Reply
  • LaughingTarget - Tuesday, April 19, 2011 - link

    Quite a bit, really. It's a lousy drafting platform. Don't try doing anything remotely related to engineering on it. Want to create a proprietary program to tie into your own business systems at work? Don't bother, you're not putting that thing on your iPad without Apple's permission. Don't bother trying to type anything lengthy up on the thing, you'll be operating, at best, on about 1/4 speed as a keyboard. It's a useless tool for accountants, field technicians needing to keep track of customer data, worthless for engineers trying to troubleshoot a power plant turbine on-site. Hell, it's even a horrible method of ringing up orders at a fast food joint.

    Go down the list of what people do for a living, the meat of the modern global economy, and you pretty much found everything the iPad can't do.
    Reply
  • kevith - Sunday, March 20, 2011 - link

    Use it as an E-reader?

    Well, only for books, that the the censors at Macintosh find good, clean and familyfriendly enough, that is.

    "When You start burning books, You will eventually end up burning people."

    That fact does not change over time...
    Reply
  • WaltFrench - Sunday, March 20, 2011 - link

    Let's be a bit more honest here: Heine was talking about government-sanctioned political violence, not commercial decisions. In fact, the considerations are almost exactly opposite.

    Commercial decisions have dozens of considerations, including authors' willingness to grant rights (e.g., Nabokov's Pale Butterfly not in any e-form), format (the wonderful Visualizing Information, also MIA) and a host of others. Freedom of speech implies the speaker's right to choose when and how he speaks; that means Apple's right to make commercial decisions about what it offers and what it does not.

    E.g., Apple no longer sells a camera, but they don't in any way restrict your ability to buy them or use them. Re books: if you like Kindle, for example, read them on the iPad. (As long as Amazon chooses to carry the work.) This is just like say, the B&N store across from my office: they don't carry titles they don't want, whether for expected lousy sales, or to keep the local Bigots United chapter from waving pitchforks at them. This freedom of Apple, which is NOT an arm of the US Government, to have its own voice, is just as important as preventing governments from banning speech.

    Maybe there is somebody at Apple who wants to treat you like a child. But about a hundred times more likely is that they simply want to do the stuff they think they do best, and some people act (childlishly!) as if Apple should run by different principles.

    PS: “Macintosh” is not the company you're talking about.
    Reply
  • vision33r - Saturday, March 19, 2011 - link

    The last thing you want is bring that $899 device in front of people and have app crashes and App drawer that doesn't work when you press it like a zillion times.

    People at work will just say you blow $899 on a netbook.

    Yes, the LCD on the Xoom is the typical 10.1" you found on Acer Netbook parts bin.

    How dare Motorola try to pass off a netbook for $899. How about the ASUS EEE Slate for $999 instead.
    Reply

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