Why Software Can Run Across Different CPU Architectures and Operating Systems: Rosetta, Universal Binaries, and Compatibility Techniques

The author poses a simple experiment: copy a Windows executable to a Mac (no run) and copy an old Intel‑based Mac app to a new ARM‑based Mac (runs). This demonstrates that differing CPU architectures and operating systems are generally incompatible.

CPU incompatibility arises because each architecture implements a different machine‑code instruction set; an x86 binary cannot be executed directly on an ARM CPU.

Operating‑system incompatibility stems from distinct system‑call interfaces and libraries; software built for one OS expects its own APIs and will not run on another without adaptation.

Apple’s Rosetta technology bridges the CPU gap by dynamically translating x86_64 instructions to ARM at runtime, allowing Intel‑based macOS apps to run on Apple Silicon.

Apple also introduced Universal Binaries, which package both x86_64 and arm64 executables in a single app bundle, enabling native execution on either architecture without translation.

For cross‑OS compatibility, tools like Wine reimplement Windows system calls on macOS (or other Unix‑like systems), allowing Windows programs to run on non‑Windows platforms.

Calculator.app/Contents/MacOS/Calculator: Mach-O universal binary with 2 architectures: [x86_64:Mach-O 64-bit executable x86_64] [arm64e:Mach-O 64-bit executable arm64e]
Calculator.app/Contents/MacOS/Calculator (for architecture x86_64):	Mach-O 64-bit executable x86_64
Calculator.app/Contents/MacOS/Calculator (for architecture arm64e):	Mach-O 64-bit executable arm64e

Beyond binary translation, source code can be compiled separately for each platform using appropriate compilers (e.g., Go, C), or compiled once to an intermediate representation executed by a virtual machine, as exemplified by Java bytecode and the JVM.

In summary, achieving cross‑platform execution requires either translating CPU instructions (Rosetta), translating OS APIs (Wine), bundling multiple binaries (Universal Binaries), recompiling source for each target, or employing a platform‑agnostic virtual machine; each approach adds a compatibility layer to bridge the inherent differences.