Is Apple Silicon Really ARM?

Introduction

Apple recently announced they were transitioning their line of Mac computers from using Intel CPUs to what they announced as Apple Silicon. This led to a lot of confusion since most people expected them to announce they would transition to the ARM CPU. The confusion arises from Apple’s market-speak where everything has to be Apple this or Apple that. Make no mistake the heart of Apple Silicon is the ARM CPU, but Apple Silicon refers to Apple’s System on a Chip (SoC) which includes a number of additional components along with the ARM CPUs. In this blog we’ll look at what Apple Silicon really is and discuss some of the current misconceptions around it.

ARM at the Core

My book “Programming with 64-Bit ARM Assembly Language” includes examples of adding ARM Assembly Language to Apple iOS apps for the iPhone and iPad. The main processors in iPhones and iPads have been redesignated as Apple Silicon chip, and the SoC used in the latest iPad is being used in Apple’s developer preview hardware of the new Mac Mini.

In fact, one of my readers, Alex vonBelow, converted all the source code for my book to run on the prototype Apple hardware. The Github repository of his work is available here. Again, this all demonstrates that ARM is at the center and is the brains behind Apple Silicon.

Other bloggers have claimed that Apple Silicon does not in fact use ARM processors since Apple customizes their ARM CPUs, rather than using off-the-shelf designs from ARM Holdings. This is true, but in fact most ARM licensees do the same thing, adding their own optimizations to gain competitive advantage. The key point is that Apple licenses the ARM CPU ISA (Instruction Set Architecture), which is the format and syntax of all the Assembly Language instructions the CPU processes, and then Apple uses ARMs software/hardware verification suite to ensure their designs produce correct results.

These other bloggers claim that Apple may stray from the ARM ISA in the future, which of course is possible, but highly unlikely. One of the keys to Apple’s success is the way they leverage open source software for much of both their operating system and development tools. Both MacOS and iOS are based on the open source Mach Unix Kernel from Carnegie Mellon University which in turn is based on BSD Unix. The XCode development environment looks Apple proprietary, but to do the actual compiling, it uses the open source tools from GCC or LLVM. Apple has been smart to concentrate their programming resources on areas where they can differentiate themselves from the competition, for instance making everything easier to use, and then using open source components for everything else. If Apple strays from the ARM ISA, then they have to take all this on themselves and will end up like Microsoft with the Windows 10 mess, where they can’t compete effectively with the much larger open source community.

Apple Silicon is an SoC

Modern integrated circuits allow billions of chips on a single small wafer. This means a single IC has room to hold multiple CPU cores along with all sorts of other components. Early PCs contained hundreds of ICs, nowadays, they contain a handful with most of the work being done by a single chip. This has been key to cell phones allowing them to be such powerful computers in such a small package. Similarly the $35 Raspberry Pi is a credit card sized computer where most of the work is done by a single SoC.

Let’s look at what Apple is cramming into their Apple Silicon SoC.

1. A number of high performance/high power usage ARM CPU cores.
2. A number of low power usage/lower performance ARM CPU cores.
3. A Graphics Processing Unit (GPU).
4. An Artificial Intelligence Processing Unit.
5. An audio DSP processor.
6. Power/performance management.
7. A cryptographic acceleration unit.
8. Secure boot controller.

For some reason, Apple marketing doesn’t like to mention ARM, which is too bad. But any programmer knows that to program for Apple Silicon, your compiler has to generate ARM 64-bit instructions. Similarly, if you want to debug a program for iPads, iPhones or the new Macs, then you have to use an ARM capable debugger such as GDB and you have to be able to interpret ARM instructions, ARM registers and ARM memory addressing modes.

It isn’t unusual for marketing departments to try and present technical topics to the general population in a way that doesn’t make sense to programmers. Programmers have to stick to reality or their programs won’t work and ignore most of what comes out of marketing departments. If you attended Apple’s WWDC a few months ago, you could see the programmers struggling to stick to the marketing message and every now and then having to mention ARM processors.

Summary

The transition of Macs from Intel to Apple Silicon is an exciting one, but don’t be fooled by the marketing spin, this is a transition from Intel to ARM. This is Apple going all-in on the ARM processor, using the same technology to power all their devices including iPhones, iPads and Mac computers.

If you want to learn more about the ARM processor and programming the new Apple devices, check out my book: Programming with 64-Bit ARM Assembly Language. Available directly from Apress, along with all the main booksellers.

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