The hard part of porting to a different platform is usually not the instruction set. It’s the OS and system abstractions. For example, if you have a program th

The hard part of porting to a different platform is usually not the instruction set. It’s the OS and system abstractions. For example, if you have a program that just does raw math and pointer arithmetic and data structure manipulation —- that is, pure computation — then porting it to a different CPU might well be trivial. Just recompile. As long as your language toolchain supports it, this will Just Work. But if your program works with the filesystem and sockets and threads, then it’s less likely to work. This is the promise of POSIX: if your program uses only what’s offered by the POSIX standard and uses those functions correctly, then it’s supposed to work on any POSIX-compliant system. Just recompile. But if your program has a GUI, or does 3D graphics, or uses special methods for high-performance networking, or accesses gyroscopes or accelerometers or touch sensors, well then you have to do work to port. And notice that this work isn’t about which CPU instruction to use. It’s about figuring out —- deciding —- what the right thing to do is, for your app, given a slightly different set of available system capabilities.