Is iPad 2 an ARM Cortex A9 or two Cortex A8s?

<img src="/sites/imore.com/files/styles/400w400h/public/images/stories/2011/03/Screen-shot-2011-03-03-at-8.56.18-AM.png" alt=Is iPad 2 an ARM Cortex A9 or two Cortex A8s?" title="Is iPad 2 an ARM Cortex A9 or two Cortex A8s?" width="400" height="214" class="aligncenter size-medium wp-image-57144" />

When Steve Jobs announced the dual-cored Apple A5 System-on-a-Chip (SoC) at the iPad 2 event, I assumed it was using an ARM Cortex A9 dual-core processor as its CPU. Last year's Apple A4 SoC used a single core, 1 GHz Cortex A8 after all, so why wouldn't the Apple A4's successor use the Cortex A8's successor? However, John Siracusa of Ars Technica raised an interesting alternative on this week's Hypercritical podcast -- what if Apple is instead use two Cortex A8 cores instead?

His argument was that, with the Cortex A9's architecture, it should be more than the 2x speed boost Steve Jobs claimed at the iPad 2 event. If it was more than 2x the speed, Apple would certainly have said so. 3x, 4x -- all look better on stage and on websites (much like the 9x graphics claim).

With previous year's 13-inch MacBook Pro, Apple stuck with old Intel Core2 Duo processors and Nvidia chipsets and when questioned about it, Steve Jobs replied that Apple thought major battery life and graphics improvements were more important that relatively minor CPU speed boosts.

Could the same be true with the Apple A5? Could Apple have stuck with the older Cortex A8 and shifted performance increases to the GPU (PowerVR SGX), all to keep that 10 hour battery life?

We'll have to wait for the teardowns to find out.

[Hypercritical]

Rene Ritchie

Editor-in-Chief of iMore, co-host of Iterate, Debug, Review, Vector, and MacBreak Weekly podcasts. Cook, grappler, photon wrangler. Follow him on Twitter and Google+.

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Reader comments

Is iPad 2 an ARM Cortex A9 or two Cortex A8s?

22 Comments

AFAIK there is no multi-core Cortex-A8. ARM hasn't designed one. So unless Apple wasted a lot of resources to make an outdated non-multi-core CPU multi-core capable (and it couldn't be called a dual-core Cortex-A8 anyway because it would be custom CPU core, just like Scorpion), the A5 consists of a dual-core Cortex-A9, just like all the other (non-Qualcomm) dual-core smartphone/tablet SoCs.

Your statement assumes they went with a dual-core processor and not with two processors in ther A5 SoC. Really the only sacrifice they'd make with that design is size because the SoC is custom made regardless of what base components the use for it.

You fail to understand CPU hardware architecture. If the A8 doesn't have SMP support in hardware, then Apple would have had to do some major rework to assure correct behavior of the independent processors (cache/memory coherence between cores, etc). It's not enough to just cut-n-paste more of the things on the SoC. If the processors were truly independent, that would essentially kill the use of threading and key frameworks like Grand Central Dispatch.
While it's theoretically possible that Apple either reworked the A8 or did some gross s/w side hacks to utilize multiple non-SMP cores, those are bend-over-backwards scenarios. It makes much more sense for Apple to utilize an SMP-aware core (i.e. A9) unless there was a major benefit to staying the course with A8.

Didn't Jobs mention "two processors" when summing up towards the end of the presentation?

if you consider that ipad 2 is designed to compete with its rivals for a year, and its rivals are using real dual core cpu right now then ipad 2 probably has dual-core Cortex-A9.

Is it cheaper to use one cortex a9 chip versus 2 cortex a8 chips? Tegra 2 more powerful than cortex 9? iPad 2 is smaller and a9 would preserve space. Would 2 a8 be faster? How would 2 a8 work? Can you add second core to a8? Would this cost more? I think a5 had a dual core a9!

Jobs is kinda right. Battery & Graphics are what really makes satisfaction in a consumer product. Let a lone, performance. Rivals just like to talk specs. But if an A4 is already as good as it is, why do you need to go through more trouble adding more speed and reducing the battery and other good stuff. Specs just like to make people think satisfaction, when at the end, it may not lead to happy conumsers.
if that even makes sense? O.o hahaha.

It sucks that people have to guess what is inside of a device that they are possibly going to spend $829 dollars on, $1000 with accessories.
Oh well I'm still getting one Friday after work lol. Even tho honeycomb looks so pretty. Cross my fingers that iOS 5 gets better notifications, widgets or info on the lock screen, a files folder like photos, gestures and wireless syncing would be nice.

The only advantage A9 would give Apple, in terms of speed, is an out-of-order instruction set. The A8 is an ordered-instruction set. Otherwise two A8's are (performance wise, for all intents and purposes) the same as one A9.
To be honest with you, it might have just come down to what they can get cheaper. That might have been two A8's - I don't know. The small gains of an unordered instruction set would not be warranted by cost increases, nor battery life.

You seemed to have ruled out the possibility of an underclocked A9. Apple have a long history of underclocking the CPU's in iOS devices in exchange for better battery life and less heat output.
I would imagine Apple's process was to put in an A9 chip and then gradually turn down the clock rate until the battery life matched that of iPad 1. The end result was a 2x faster iPad.

I haven't listened to this week's Hypercritical yet, but I have seen Sunspider javascript benchmarks for the iPad 2. And they are for the most part identical to the Motorola Xoom's score of around 2100 ms, which is indicative that Apple's got an Cortex-A9 core type of processor.
Other things:

  1. Totally excise the idea of Apple using 2 uni-core Cortex-A8s from your mind. The idea at its most optimistic, harkening back to the Pentium D days, is a non-starter on basically every single level.
  2. @Mike111 - yup. The Cortex-A8 is a single processor architecture. It doesn't support cache coherency/snooping. Apple would have to put in a lot of work to get it to be cache coherent, when the Cortex-A9 architecture has been sitting there. The gains would have to be amazing for Apple to embark on its own design. (I would love it if Apple found some great IPC gains, but they really want >IPC for
  3. The simplest explanation is that the Apple A5 has a dual-core ARM chip with Cortex-A9 cores sharing a single L2 cache. Everything else is UFO-ology.
  4. Same thing on the RAM. It's likely got 512 MB.
  5. Apple has never mentioned what processor is in iDevices outside of the generic branding stuff. I recall of only one instance which was in March of 2008 when Forstall said the original iPhone had PowerVR MBX graphics, and I'd call that generic branding. It was unusual because they never mentioned anything specific about CPU or GPU outside of "ARM" before. For the A4, it took iFixit to figure out it used a Cortex-A8 CPU core, than some snooping some more that Intrinsity got it to clock up to 1 GHz. I don't think they mentioned the 3GS had a Cortex-A8, only that it was 2x as fast as the 3G.

I agree on the RAM. They probably don't want to talk about it because other devices are touting 1GB. 512MB will be enough, but staying staying at 256MB would be insane. We'll know soon enough.

Well, that's kind of selective reasoning (they don't mention it because competing tablets have more). It's probably true, but consider the GPU power.
They said the graphics is up to 9x as powerful. That's 9x! Almost an order of magnitude. And that's all they said about it. You'd think they would say something more about it. Adreno 220 won't be as fast (Snapdragon). PowerVR 540 won't be as fast (OMAP?). Mali won't be as fast (Exynos). Anandtech has already did some benching on the Tegra 2 GPU and its only a little bit faster than the PowerVR 540.
You don't see order of magnitude increases in computing in a 1 year time scale at all. Mostly 3 years: a doubling every 12 months. But the real cycle is a doubling in transistors every 18 months, so it's really over 4 years.
It's likely Apple is only talking about 1 metric (tri/sec or whatever) and applications won't see that as I/O, RAM and CPU performance hasn't increased as much, but still, 9x!

One website said it was confirmed that the CPU was a dual core Cortex-A5. That may account for the 2x processing power, but it would be very quick to market for the Cortex-A5. I think they were just confused by the similarity between Apple A5 and ARM Cortex-A5

There is no such thing as a dual-core Cortex A8, the CPU was never built to work with another core. Can only be Cortex A9, no need to debate this!