What Is Apple’s Rosetta 2 & How It Works Explained


Apple’s Rosetta 2 allows M1 Macs to run Intel apps, sometimes faster than on a 2020 Intel Mac, but how is this possible when running via emulation?

When Apple announced that its newest 13-inch MacBook Air, MacBook Pro and Mac mini would be powered by its M1 chip, it told existing Mac owners that the Intel apps would still run just fine and in some cases even faster. Emulators typically slow down performance significantly, but something about Apple’s hardware and software seems to make the impact negligible.

The M1 chip is still making headlines for offering blazing speed while sipping power gently. The newest 13-inch MacBook Pro, for example, beats the 1.7GHz quad-core Intel Core i7 version that came out a few months earlier, boasting nearly three times the CPU speed and up to five times the graphics performance. At the same time, efficiency has increased to offer up to 20 hours of battery life. Some had concerns about whether the new chip would work with existing apps and how much performance would suffer if Intel apps were running through an emulator.

Related: M1 MacBook Air Benchmarks Suggest Apple Mac Silicon Is The Chip To Beat

Rosetta 2 is the name of Apple’s emulator/translator software. The most basic type of emulation is to load apps designed for other computer systems or games into memory and interpret each instruction in a way that makes sense to the processor in use. In cases where a common operating system (OS) is used on both the physical hardware and the virtual system being emulated, such as with older and newer Mac computers, any calls to the operating system can execute at full speed, without the emulator being involved. Depending on how the app is coded, the emulator may continue on to the next instruction or wait for a response from the OS. This means most user input, graphics operations, file access, and other macOS standard features are handled by native code. That’s part of the reason why Apple can claim that some Intel apps that require heavy use of graphics processing actually perform better under Rosetta 2 on the M1 than they did on an Intel Mac.

Other Rosetta Techniques

Apple M1 Mac mini Rosetta Stone On-screen

Going beyond standard emulation, Rosetta 2 does some of the work in advance. When first installing the app via the Mac App Store or other Apple recognized installer, much of the Intel code is translated into M1 instructions before it is even run. If installed via a third-party installer such as Microsoft’s installer for the Intel version of Office, the translation happens upon the first run of the app. This isn’t as efficient as if the app was written for the M1 in the beginning and the emulator is still needed at runtime for code that couldn’t be handled in advance, but Rosetta 2 does a remarkable job of optimizing code that was developed for a whole different CPU architecture and translating on the fly when necessary.

Based on various reports and benchmarks, apps running through Rosetta 2 achieve about 80 percent of the performance of a Native M1 app. Of course, this will depend on how the app was coded and how much is handled with macOS calls. When Intel app performance is compared between a previous generation Intel Mac and a current-generation M1 Mac using emulation, the newer Mac may still be faster. Newer models typically have better performance, but the M1 seems to have surprisingly fast speed even when emulating Intel processors through Rosetta 2.

Next: Universal Apps: Best macOS Apps Compatible With M1 Macs

Source: Apple

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Updated: November 23, 2020 — 12:26 pm

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