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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  • george1924 - Saturday, March 19, 2011 - link

    Seems to be fixed now Reply
  • Anand Lal Shimpi - Saturday, March 19, 2011 - link

    Thanks for the correction :)

    Take care,
    Anand
    Reply
  • drugos - Saturday, March 19, 2011 - link

    As usual, one of the most comprehensive reviews on the net. Thanks guys! Reply
  • Bosh - Sunday, March 20, 2011 - link

    Yes, as usual ! Reply
  • PrinceGaz - Saturday, March 19, 2011 - link

    Who buys worthless over-priced rubbish like the iPad, apart from hipsters/dickheads? I can understand the appeal of it to them, and I've nothing against dickheads who love them, but what purpose do they serve to the rest of us?!?

    It's incapable of being used for real work so basically useless except as a toy when out and about, but too large to be carried around in anything smaller than what a small laptop could be carried in, so what it can do when on the move may as well be done on a smartphone.
    Reply
  • B3an - Saturday, March 19, 2011 - link

    Cant beleive i'm saying this about an Apple product... but the iPad 2 isn't expensive for the hardware. Look at the Motorola Xoom which is lot more expensive for marginally better hardware, although the iPad 2 has better hardware in some areas. The thing is though Apple can sell the iPad 2 at little profit because they just make the money from app sales. So it's hard for other tablet makers to compete on price.

    I agree with everything else though.
    Reply
  • shabby - Saturday, March 19, 2011 - link

    The ipad2 is expensive, imagine if asus took their $250 10" netbook and removed the keyboard, replaced the hard drive with a sd card for memory, and ditched the intel mobo/cpu for a slower soc this thing would cost maybe $150.
    The only reason these devices have these prices is because that's how much people are willing to pay for them.

    As for the xoom, motorola for some reason thinks they can charge a premium for it, they certainly are smoking some good shit. These phone manufacturers will fail with their expensive tablets.

    Once asus and other netbook manufacturers start saturating the market with android tablets you'll start seeing cheaper solutions.
    Reply
  • jalexoid - Saturday, March 19, 2011 - link

    That is not true. FOB price for the 16GB XOOM clone(proper quality clone, not a knockoff) is about $330. Smaller components cost more. Reply
  • WaltFrench - Sunday, March 20, 2011 - link

    “The only reason these devices have these prices is because that's how much people are willing to pay for them.”

    Showing off the fact that we've had Econ 101, are we?

    Perhaps there's some object/service that operates differently that you'd care to mention.
    Reply
  • kukabuka - Saturday, March 19, 2011 - link

    Well, I for one think tablets are really great when you don't need a keyboard or a fast processor or a lot of storage. Which would be never. If the iPad sells way better than the Xoom, I'd say your theory about hipsters/dickheads being the only market group for tablets is confirmed. Reply

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