You can compile your binary for multiple architectures, check the type of processor and give it the appropriate binary. They also have the LLVM option so that

You can compile your binary for multiple architectures, check the type of processor and give it the appropriate binary. They also have the LLVM option so that old binaries keep working on new architectures without recompiling and rewriting NaCl for them, but it has downsides http://blog.chromium.org/2010/03/native-client-and-web-portability.html http://blog.chromium.org/2010/03/native-client-and-web-porta... The reason they didn't go with LLVM as the main approach was performance. Google wants there to be no distinction between desktop and web apps, and for web apps to have even 60% of desktop performance is still unacceptable. 90+% is more like it.