Rosetta 2 is Apple’s key to making the ARM transition less painful

Earlier this week, on what Tim Cook called a “historic day,” Apple announced that it is moving Macs away from Intel processors to its own silicon chips. Apple’s first Mac with silicon will arrive by the end of 2020, but Apple expects the full transition process to take two years.

Newer Macs will use arm64, the same processor architecture as recent iOS devices (Intel-based Macs use an architecture called x86-64). It’s an exciting move, because it means they’ll be able to run iOS and iPadOS apps alongside those designed for macOS. But it also means that applications that were developed for Intel’s architecture originally will not work natively on future hardware from Apple.

This is where Rosetta 2 comes in: it’s an emulator built into macOS Big Sur that will allow Mac ARMs to run old Intel applications. Rosetta 2 essentially “translates” the written instructions for Intel processors into commands that Apple’s chips can understand. Developers will not need to make changes to their old applications; they’re just going to work. (The original Rosetta was released in 2006 to ease Apple’s transition from PowerPC to Intel. Apple has also said it will support x86 Macs “for years to come”, as far as updates go. The company switched from PowerPC to Intel chips in 2006, but discontinued support for the former in 2009; OS X Snow Leopard was Intel-only.)

As a user, you do not interact with Rosetta; he does his work behind the scenes. “Rosetta 2 is primarily there to minimize the impact on end users and their experience when they buy a new Mac with Apple Silicon,” says Angela Yu, founder of the App Brewery School of Software Development. “If Rosetta 2 is doing its job, your average user shouldn’t notice it exists.”

There is one difference you might notice, however: the speed. Programs running under the original Rosetta generally ran slower than those running natively on Intel, because the translator needed time to interpret the code. First benchmarks found that popular PowerPC applications, such as Photoshop and Office, performed at less than half of their native speed on Intel systems.

We will have to wait and see if the applications in Rosetta 2 achieve similar performance. But there are several reasons to be optimistic. First, the original Rosetta converted every instruction in real time, as it executed them. Rosetta 2 can convert an app directly upon installation, creating an ARM-optimized version of the app before you open it. (It can also translate on the fly for applications that cannot be translated ahead of time, such as browser processes, Java, and JavaScript, or if it encounters other new code that has not been translated in advance. time of installation.) With Rosetta 2 loading much of the work, we can see better performance of the translated applications.

Screenshot: Dan Seifert / The Verge

The demos also looked promising. Apple showed Rosetta using Maya animation software and the game Shadow of the Tomb Raider in 1080p; both seemed functional in the speech.

There are a few caveats, however.

First, Rosetta 2 is not intended to be a long term solution. Apple hasn’t said how long this will last; Rosetta, released with OS X Tiger, was not discontinued with OS X Lion until three versions later. It’s a tool that will ease Apple’s transition period, but Apple certainly intends its developers to jump into the native ARM ports of their x86 apps as soon as possible. Apple’s own apps, including Final Cut Pro and Logic, already work natively on ARM. The company has previously announced developer transition kits with an ARM processor inside to help app makers update and test their software – and it noted in the speech that Microsoft is already working on Office and Adobe is working on Creative Cloud. Apple showcased native versions of Word, Excel, PowerPoint, Lightroom CC, and Photoshop, as well as its own Final Cut Pro at the WWDC keynote.

That said, Apple clearly understands that not all developers will have ports ready for the first ARM launch – and customers who buy the first ARM systems in the fall will want to use their favorite programs immediately. Rosetta 2 also means developers don’t need to scramble to re-optimize their products as the first Mac ARMs come out. (The process of porting macOS apps to Apple’s silicon is beyond the scope of this guide, but you’ll find detailed instructions on Apple Developer Website.)

“Changing the language spoken by the processor is a huge deal,” says Ken Gillette, co-founder and CTO of Pocket Prep, a mobile test prep company that has developed over 100 apps for the Apple ecosystem. “It would be very difficult if every application had to be updated before the new computers were available. It would result in a big effort to make changes in a short period of time. ”

“[Rosetta] will make the process of buying a new Mac transparent to end users, ”says Gillette. “If Apple didn’t do this, the process would be much more painful, as many of the apps consumers use on a daily basis would be missing from their brand new machines. “

Screenshot: Sean Hollister / The Verge

Another thing to note is that the motor will not support everything either. It is not compatible with some programs, including virtual machine applications, that you can use to run Windows or another operating system on your Mac, or to test new software without affecting the rest of your system. (You will also not be able to run Windows in Boot Camp mode on ARM Macs. Microsoft only licenses the ARM version of Windows 10 to PC manufacturers.) Rosetta 2 also cannot translate. kernel extensions, which some programs use to perform tasks for which macOS does not have native functionality (similar to drivers in Windows).

Third, even though Rosetta 2 is fully functional, questions remain about how well Mac ARMs work. In its speech, Apple highlighted the effectiveness of its new chips, saying they “will give the Mac the best performance per watt in the industry.” The company also promised a better graphics experience, machine learning capabilities, and better battery life. But it got around the raw power issue. So while ARM Macs may be more efficient than their Intel predecessors, they can also be less powerful. Apple also didn’t say whether it plans to produce its own GPUs or whether its CPUs will interface with third-party GPUs.

The ARM processors we’ve seen on Windows PCs like the Surface Pro X have outperformed their Intel competitors in battery life and LTE compatibility. But we also encountered performance issues with ARM PCs, although this is at least in part due to the fact that the emulation layer Microsoft uses to run x86 apps on ARM can only run 32-bit Windows apps. (not modern 64-bit x86 applications) and many 32-bit programs are significantly slower than 64-bit programs.

If everything works as Apple promised, Rosetta 2 means that hopefully none of this mess will happen with macOS.