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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  • podperson - Monday, March 21, 2011 - link

    Just admit that most PCs are used as toys. Heck, the whole reason the personal computer took off (in homes) was as a games platform.

    Most of the people I see with PCs are using them to surf the web, watch youtube, update facebook, or mess around with digital media. Where I work there are Macs and PCs available to the public with 27" monitors all open to Facebook (hint, it's a university). Exactly what is this "work" you need to do on PCs? For most people it's a little bit of text editing now.

    For some kinds of things the iPad is markedly superior ergonomically to a PC (or even a tablet computer or WACOM tablet display) — e.g. sketching or various musical apps. For others a PC is markedly superior. For still others one or the other is completely useless.
    Reply
  • michael2k - Monday, March 21, 2011 - link

    Except it isn't bulky nor underpowered for many things.

    I have a 2006 G4 iBook that is lower performance than a 2010 iPad 2. If the iPad 2 is a toy, then so is just about any early 2006 computer, including older Pentium M based laptops.

    It is also far less bulky than self same 4 year old computers, with trivially 2 to 3 times the battery life.

    I paid $500 so that my wife can follow my kids around, but still have a computer she can put in her purse. Without the iPad, she would have indeed settled for an iPod touch, but a netbook with a hinge? Too short a battery life and too hard to manage (Windows XP, Windows Update, AV, etc) for the harried housewife/homemaker
    Reply
  • bigboxes - Monday, March 21, 2011 - link

    Just how big is her purse? As for battery life I think you are looking through rose colored glasses in emphasizing the positive qualities that your device holds. As long as the device lasts until you get home to plug it in (maybe even your vehicle) it will suffice. The iPad is too bulky and not functional enough too do day to day tasks. As I said earlier, the authors point this out.

    As much as we want these cute devices to succeed we find ourselves using other devices that are far more practical. I've made the same mistake myself in the past. Anyone remember the Sony Clie? Another proprietary underpowered overpriced device. I believe I paid $500 for it. It gathered dust for years until I finally put it in a box. There's the cool factor and then there's reality. Do you set it out for your friends' visits or do you actually get x value out of it?

    Also, you are going to be carrying your phone with you already. Why carry both devices with you when one doesn't have more functionality over the other? I would think that the balance for function belongs to the smartphone (phone service is more valuable than screen size).
    Reply
  • michael2k - Monday, March 21, 2011 - link

    Her purse is big enough to hold an iPad, a wallet, another smaller purse, a phone, keys, two Capri Suns, two candy bars, a small bag of chips, and a couple of diapers.

    As for battery life, that's exactly what the iPad is; it lasts as long as it needs to until it gets home to be plugged in. I cannot find a laptop under 2 pounds with similar battery life. The minimum requirement is 6 hours.

    I carry my phone because I am more like Anand than not. She carries the iPad because she isn't like Anand, at all. It would be the equivalent of me driving a Civic and her driving a minivan; surely the very concept of a soccer mom and her requirements being different than a 9-5 commuter isn't lost on you?
    Reply
  • bigboxes - Monday, March 21, 2011 - link

    So, we can officially say this is the official tablet of soccer moms everywhere. Yay.

    She carries it around not because she is unlike Anand. She carries it around because she has a strong back!
    Reply
  • vol7ron - Sunday, March 20, 2011 - link

    A lot of the "sales" are from the retail outlets and not-necessarily the end-user consumer. There's people that buy it to sell to China or other Asian countries that buy it for double it's price; there are a plethora of reviewers these days; there are the people with mass amount of wealth that buy up anything just because they can; and then the hipsters that want to be cool and fit in. It reminds me of the episode of South Park with the smug Prius drivers.

    I'm not saying this isn't a bad device and it's mobility makes it beneficial in many regards. But the price of its mobility does not make it as attractive as it would be at the lower price (~$250). I'm not saying it should go for $100, but you're nearing the $1000 end of the spectrum for these devices and way over that for the necessary apps and accessories.
    Reply
  • crunc - Monday, March 21, 2011 - link

    I don't know why I'm getting into this argument, but all the iPads, including iPad 2's, that I'm seeing out in the world would seem to dispell your notion that no one is actually buying them for their own use. I saw 3 of them within 5 feet of me on the train this morning, for example. In 3 weeks time or so I'll be another one on the train with one, and also using it at home. I don't own a laptop. I wouldn't mind a laptop, but I'd rather have an iPad. It is, for me, far more comfortable to use then a laptop. Even the excellent trackpads on MacBooks don't compare to the entirely touch-based interface of the iPad. Obviously they aren't for everyone, but for some these are a great choice. I don't expect to write a book on it, but I then don't write books. If I ever decide to write a book, maybe I'll get a laptop. Reply
  • Ushio01 - Sunday, March 20, 2011 - link

    It's a fasion accessory just like the iphone, to be with the "in crowd" you have to have apple products that's all there is to it. Everyone on here must know at least someone who bought an iphone and then use it only for calls and texts, I know dozens of people who have done this. Reply
  • crunc - Monday, March 21, 2011 - link

    Actually, no, I don't know anyone who has an iPhone that only uses it for texts and phone calls. Everybody I know who has one uses it for virtually everything, myself included. In fact, I rarely text and only occasionally make phone calls (mostly of the, "should I pick up a pizza?" variety). You go on living in your little dream world, though. I won't stop you. I have an order in for an iPad 2 and I'm really looking forward to it. I love my iPhone and I want something akin to a laptop, but that isn't that, because the iOS interface is fantastic and the devices are more comfortable for me to use. Sure, there's some shortcomings to the platform, but they are overwhelmed by the multitude of positives. Reply
  • sarahtim - Sunday, March 20, 2011 - link

    I think this sort of comment represents a failure of imagination. As iPads sell million after million you have to adjust your idea of how many hipsters there are...
    Other people are different from you.
    Speaking for myself; I find my iPad extremely useful. I use it for a number of hours each day. I don't find it clunky. To me, and this is a very personal thing, the cost was of little consequence. While it is poor taste to blurt out your relative wealth when many folks are having a rough time of it, it is the only way to answer your comment. Further, I consider iPads to be very good value. I bought the bottom of the line iPad 1. It does everything I want. The bulk of its time is spent streaming video via the Air Video app.
    I represent a single data point - as do you. I fully appreciate that an iPad is a useless paperweight to you. No problem. When I use my iPad I do it in private. I don't discuss my ownership with others. I don't think I'm clever or a better person because I have one.
    You would have to look at me for a very long time before you thought of a hipster. Trust me on this. :-)
    Reply

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