Apple A5X

Apple is known for dancing around the speeds and feeds for its products. The Cupertino-based company prefers to speak in more easy to understand terms like, “twice as fast,” or “amazing speeds.” When technical terms do get thrown out, they are usually those that will grab people’s attention; something already weaving its way through the technological zeitgeist. When the new iPad was announced, Apple unveiled the A5X ARM system-on-a-chip (SoC) with it. Apple repeatedly referred to the chip as possessing quad-core graphics, which is an unusual usage of “quad-core.”

As a result of this marketing message, many users have become a little confused about what quad-core means, and if the A5X is a quad-core part in the same way Nvidia’s Tegra 3 is. The fact that Apple specifically called out comparisons to Tegra 3 in the keynote didn’t help that. So let’s take a closer look at what the A5X really is.

What makes an ARM-based SoC useful in mobile devices is that it incorporates multiple vital system elements onto a singe die. Almost all chips contain the application processors (ARM cores), GPU, and memory controller. Other components like cellular radios can also be built in. When we talk about quad-core, we mean quad-core processors, not graphics.

Apple’s A5X still uses the same dual-core design for the ARM Cortex-A9 processing cores that it did last generation. Nvidia does still use Cortex-A9, but its Tegra 3 part has four cores, thus quad-core. It would be very misleading to consider the Apple part to be quad-core because of the four graphics cores — the core counting game has always referred to processors up to now.

There is a lot of debate currently on the merits of quad-core processors in mobile devices. It’s still up in the air whether or not developers will take sufficient advantage of the technology to warrant the increased power draw. Graphics processors, by their very nature, are more parallel and tend to benefit from more cores. Many desktop graphics cards have hundreds of cores, often called stream processors. So unlike increasing the number of processors, more GPU cores can reliably improve performance.

The A5X GPU is likely the PowerVR SGX543MP4 (the Apple A5 used an SGX543MP2, which you may notice was not called out as dual-core). Apple was pushing the quad-core graphics so hard, it even cited its new A5X as being four times faster than Tegra 3. It’s not clear how Apple was making that measurement, and Nvidia has asked for proof on the matter. It’s possible Cupertino is adding the theoretical maximum calculations of the four GPU cores to get a sketchy number representing total performance. This number would be roughly four times that of the Tegra 3, but is likely unrelated to real life performance.

At the end of the day, the new iPad is not a quad-core device by the accepted definition any more than Samsung’s Galaxy S II is with its Mali quad-core GPU. Apple is slavishly committed to maintaining smooth performance and fast response times no matter the hardware, so perhaps the distinction doesn’t matter. The new iPad is likely to perform as well or better than any Tegra 3 device. If anything, Apple’s adoption of the term quad-core is just an admission that the spec war does have some affect on consumer sentiment