Microsoft today announced ARM64EC, a new way for developers to build native apps for Windows 11 on ARM. This technology is being used by Microsoft Office and Visual Studio, and it lets developers mix and match native ARM64 code with emulated x86/x64 code in the same process.
“ARM64EC is a new application binary interface (ABI) for Windows 11 on ARM that runs with native speed and is interoperable with x64,” Microsoft’s Marc Sweetgall explains. “An app, process, or even a module can freely mix and match ARM64EC and x64 as needed. The ARM64EC code in the app will run natively while any x64 code will run using Windows 11 on ARM’s built-in emulation.”
In the past, developers interested in creating apps that ran on Windows on ARM were forced to recompile the entire app. With ARM64EC, developers can bring over parts of an existing app one at a time, identifying those codebases that would benefit the most from running natively. The rest of the app, meanwhile, will simply run in emulated mode. Over time, developers can choose to recompile more of their apps as ARM64EC, as needed, improving the PC’s performance and battery life.
ARM64EC also makes it much easier to port over apps that support add-ons and third-party dependencies. Both Office and Visual Studio fall into this category.
“We’re motivated by the potential of ARM64EC and excited to see the kinds of apps developers can build for Windows 11 on ARM using this technology,” Sweetgall says. “Internally, we’ve rebuilt the binaries of Windows 11 on ARM itself with ARM64EC so that any system code loaded by x64 apps runs with native speed. In addition, the Office team is using ARM64EC in the coming 64-bit Office for ARM so that existing x64 plugins will work seamlessly.”