Jun 272020

So Apple has announced that it is replacing Intel processors with ARM processors in its Mac machines. And as a result we’re going to be plagued with awful puns endlessly until we get bored of the discussion. Sorry about that!

This is hardly unexpected – Apple has been using ARM-based processors in its iThingies for years now, and this is not the first time they have changed processor architectures for the Mac. Apple started with the Motorola 68000, switched to the Motorola/IBM Power architecture, and then switched to Intel processors.

So they have a history of changing processor architectures, and know how to do it. We remember the problems, but it is actually quite an accomplishment to take a macOS binary compiled for the Power architecture and run it on an Intel processor. It is analogous to taking a monolingual Spanish speaker, providing them with a smartphone based translator and dropping them into an English city.

So running Intel binary macOS applications on an ARM-based system will usually work. They’ll be corner cases that do not of course, but these are likely to be relatively rare.

But what about performance? On a theoretical level, emulating a different processor architecture is always going to be slower, but in practice you probably won’t notice.

First of all, most macOS applications very often consist of a relatively small wrapper around Apple-provided libraries of code (although that “wrapper” is the important bit). For example, the user interface of any application is going to be mostly Apple code provided by the base operating system – so the user interface is going to feel as snappy as any native ARM macOS application.

Secondly, Apple knows that the performance of macOS applications originally compiled for Intel is important and has Rosetta 2 to “translate” applications into instructions for the ARM processors. This will probably work better than the doom-sayers expect, but it will never be as fast as natively compiled code.

But it will be good enough especially as most major applications will be made ARM natively relatively quickly.

But there is another aspect of performance – are the ARM processors fast enough compared with the Intel processors? Well, the world’s fastest supercomputer runs on the ARM processors, although Intel fanboys will quite rightly point out that a supercomputer is a special case and that a single Intel core will outperform a single ARM core.

Except that with the exception of games, and specialised applications that have not been optimised for parallel processing, more cores beats faster single cores.

And a single ARM core will beat a single Intel core if the later is thermally throttled. And thermals has been holding back the performance of Apple laptops for quite a while now.

Lastly, Apple knows that ARM processors are slower than Intel processors in single core performance and is likely pushing ARM and themselves to solve this. It isn’t rocket science (if anything it’s thermals), and both have likely been working on this problem in the background for a while.

Most of us don’t really need ultimate processor speed; for most tasks merely the appearance of speed is sufficient – web pages loading snappily, videos playing silkily, etc.

Ultimately if you happen to run some heavy-processing application (you will know if you do) whose performance is critical to your work, benchmark it. And keep benchmarking it if the ARM-based performance isn’t all that good to start with.

And most of these tasks can be performed fine with a relatively modest modern processor and/or can be accelerated with specialised “co-processors”. For example, Apple’s Mac Pro has an optional accelerator card that offloads video encoding and makes it much faster than it would otherwise be.

Apple has a “slide” :-

That implies that their “Apple silicon” processors will contain not just the ordinary processor cores but also specialised accelerators to improve performance.

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