What is Rosetta 2?
Rosetta 2 is Apple's translation layer that allows Intel (x86-64) apps to run on Apple Silicon (ARM64) Macs. It's built into macOS and works automatically.
How Translation Works
When you launch an x86 app:
- First Launch: Rosetta translates the binary to ARM64
- Caching: Translated code is cached for future use
- Execution: ARM64 code runs natively
This translation happens once and is stored, so subsequent launches are faster.
Performance Impact
| Scenario | Performance vs Native |
|---|---|
| CPU-bound tasks | 70-90% |
| GPU-bound tasks | 90-100% |
| Memory-heavy apps | 80-95% |
| First launch | Slower (translation) |
When Rosetta Matters
Noticeable Impact:
- Compilation (building code)
- Heavy computation
- Complex simulations
Minimal Impact:
- Everyday apps
- Web browsers
- Office software
- Most games
Checking If an App Uses Rosetta
- Open Activity Monitor
- Look at the Architecture column
- "Intel" = Rosetta, "Apple" = Native
Or right-click app > Get Info > check "Open using Rosetta"
Native vs Universal Apps
- Native ARM64: Best performance
- Universal Binary: Contains both, runs native
- Intel Only: Requires Rosetta
The Future of Rosetta
Apple hasn't announced an end date, but:
- Most major apps now have native versions
- New apps should always be Universal
- Rosetta will likely remain for legacy support
