Apple walks Ars through the iPad Pro’s A12X system on a chip

BROOKLYN—Apple's new iPad Pro sports several new features of note, including the most dramatic aesthetic redesign in years, Face ID, new Pencil features, and the very welcome move to USB-C. But the star of the show is the new A12X system on a chip (SoC).

Apple made some big claims about the A12X during its presentation announcing the product: that it has twice the graphics performance of the A10X; that it has 90 percent faster multi-core performance than its predecessor; that it matches the GPU power of the Xbox One S game console with no fan and at a fraction of the size; that it has 1,000 times faster graphics performance than the original iPad released eight years ago; that it's faster than 92 percent of all portable PCs.

If you've read our iPad Pro review, you know most of those claims hold up. Apple’s latest iOS devices aren’t perfect, but even the platform’s biggest detractors recognize that the company is leading the market when it comes to mobile CPU and GPU performance—not by a little, but by a lot. It's all done on custom silicon designed within Apple—a different approach than that taken by any mainstream Android or Windows device.

But not every consumer—even the "professional" target consumer of the iPad Pro—really groks the fact this gap is so big. How is this possible? What does this architecture actually look like? Why is Apple doing this, and how did it get here?

After the hardware announcements last week, Ars sat down with Anand Shimpi from Hardware Technologies at Apple and Apple’s Senior VP of Marketing Phil Schiller to ask. We wanted to hear exactly what Apple is trying to accomplish by making its own chips and how the A12X is architected. It turns out that the iPad Pro's striking, console-level graphics performance and many of the other headlining features in new Apple devices (like FaceID and various augmented-reality applications) may not be possible any other way.

A top-level view of the A12X

The A12X is, of course, closely related to the A12 from the iPhone XS, XS Max, and XR. The latter was the first silicon made in a 7nm process available in a consumer device, and this is the first for a tablet.

The A12X is made up of many components. We'd love to dive deep into exactly how this architecture works, but Apple is generally not forthcoming with details like that. Anandtech recently ran a detailed analysis of an A12 die shot among other things, but we don't have anything like that for the A12X yet. Still, we know the big picture. To that end, components of the A12X include:

• A CPU (central processing unit), which carries out most instructions that are not specialized to other processing units.
• A GPU (graphics processing unit), which handles graphics, from display of the home screen to effects in 3D games to assets for augmented reality applications
• The Neural Engine, which handles neural network and machine learning-related tasks
• An IMC (integrated memory controller), which efficiently manages data going in and out of memory.
• An ISP (image signal processor), which analyzes images created when you take a photo and processes them, improves them, and more.
• The Secure Enclave (also SEP, or secure enclave processor), which handles sensitive data like biometric identifiers in such a way that it is difficult for someone undesirable to access it.
• There are several other components, like the display engine, a storage controller, an HEVC decoder and encoder, and more, that we won't get into much detail about here.

Chief among this list are the CPU, GPU, and the Neural Engine, so we'll focus a bit more on those.

The CPU

The iPad Pro's CPU has eight cores—four focused on performance, and four focused on efficiency. And unlike some earlier Apple chips, all cores can be active at once. This is the first device in this product line that uses this many cores simultaneously.

“We've got our own custom-designed performance controller that lets you use all eight at the same time,” Shimpi told Ars. “And so when you're running these heavily-threaded workloads, things that you might find in pro workflows and pro applications, that's where you see the up to 90 percent improvement over A10X.”

For single-core performance, Apple's marketing materials claim that the A12X is 35 percent faster than the A10X. We've come a long way from the 412MHz single-core CPU manufactured by Samsung to Apple's specifications for the original iPhone in 2007.

We tested the A12X for our iPad Pro review, so let's look at those benchmarks to verify those claims. First, here are some basic specifications on every device included in the tests.

Tablets

Model	SoC
12.9-inch 2018 iPad Pro	Apple A12X
10.5-inch 2017 iPad Pro	Apple A10X
12.9-inch 2016 iPad Pro	Apple A9X
2018 iPad	Apple A10
Samsung Galaxy Tab S4	Qualcomm Snapdragon 835

Phones

Model	SoC
iPhone XS	Apple A12
iPhone X	Apple A11
iPhone 7	Apple A10
Google Pixel 3 XL	Qualcomm Snapdragon 845

Desktops and laptops

Model	CPU	GPU
2018 15-inch MacBook Pro with Touch Bar	Intel Core i9-8950K at 2.9GHz (4.8GHz Turbo)	AMD Radeon Pro 560X 4GB GDDR5
2017 15-inch MacBook Pro with Touch Bar	Intel Core i7-7820HQ at 2.9GHz (3.8GHz Turbo)	AMD Radeon Pro 555 2GB GDDR5
2016 15-inch MacBook Pro with Touch Bar	Intel Core i7-6820HQ at 2.7GHz (3.6GHz Turbo)	AMD Radeon Pro 455 2GB GDDR5
2017 iMac Pro	Intel Xeon W at 3GHz (4.5GHz Turbo)	AMD Radeon Pro Vega 64 16GB HMB2
2017 iMac (5K)	Intel Core i7-7700K at 4.2GHz (4.5GHz Turbo)	AMD Radeon Pro 580 8GB GDDR5
2018 Dell XPS 15 2-in-1	Intel Core i7-8705G at 3.1GHz (4.1GHz Turbo)	AMD Radeon RX Vega M GL 4GB HMB2

And now for the results.

We didn't quite record the claimed 35 percent improvement in single-core performance (though this is just one benchmark), but it's fairly close. The multi-core claim also checks out.

This performance is unprecedented in anything like this form factor. In addition to the ability to engage all the cores simultaneously, there's reason to believe that cache sizes in the A12, and likely therefore the A12X, are a substantial factor driving this performance.

You could also make the case that the A12X's performance in general is partly so strong because Apple's architecture is a master class in optimized heterogeneous computing—that is, smartly using well-architected, specialized types of processors for matching specialized tasks. Though the A12X is of course related to ARM's big.LITTLE architecture, Apple has done a lot of work here to get results that others haven't.

Unfortunately, Apple wouldn't discuss any of that in too much detail with us. Whatever the specifics, this chart does a particularly good job of illustrating why this is remarkable:

The iPad Pro outperforms every MacBook Pro we tested except for the most recent, most powerful 15-inch MacBook Pro with an 8th generation Intel Core i9 CPU. Generally, these laptops cost three times as much as the iPad Pro.

"You typically only see this kind of performance in bigger machines—bigger machines with fans," Shimpi claimed. "You can deliver it in this 5.9 millimeter thin iPad Pro because we've built such a good, such a very efficient architecture."