The iPad A4 system on chip

Posted on 2010/01/30

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Apple announced their tablet and its specifications to the tech world, and the tech world happily started to tear it apart and understand how it works. Engadget has one of the most complete pages about the details.

I’m particularly interested in the central processing chip, the Apple A4.

MacWorld explains some business facts that could be related to the system-on-chip in question. Great emphasis is put on Apple acquiring P.A.Semi in 2008;  this start-up created a power-efficient microprocessor from scratch: the PWRficient(the name says it all), and while it is very implausible that Apple used their architecture in the iPad (because the OS is the same as the iPhone’s) there is no doubt that P.A.Semi has the know-how and the expertise to improve the energy consumption of a chip architecture to the point of 10 hours of usage or 300 hours of stand-by.

Anand Lal Shimpi analyzes the hardware, here’s an excerpt of his considerations (full article here):

Given the fact that it runs the iPhone OS and nearly all iPhone apps, I’m guessing the A4 is ARMv7 based. It’s possible that Apple engineered its own architecture for the A4, but more likely that it simply took an existing ARM design and modified it to suit its needs.

If Apple wanted to save cost it would’ve gone with a Cortex A8 based processor, or if it wanted more performance it would be something more A9 like.

[…]

I’m going to say that there’s a good chance that the A4 is much closer to the A9 in terms of performance. If it’s not an A9 itself, it may be Apple’s own out-of-order design.

It is an educated guess and I believe it’s the right answer, given what we know; I am more inclined to say that the A4 is not a single-core Cortex-A9 but a multi-core, given the extraordinary power efficiency, but the fact that the OS seems almost exclusively single-task lessen the probability of this hypothesis.

This article instead reports that they received the information that the A4 contains a Cortex-A9 and an ARM Mali Graphic Processing Unit, or at least ARM licensed its CPU and GPU technology to Apple. It is clear that an advanced GPU has been used because of the smoothness of the user experience seen on videos, and this technology must also be power efficient given the iPad battery life.

Unfortunately, we can only keep guessing using these small chunks of information, until Apple decides to reveal the A4 secrets.

Posted in: Hardware