I’m no expert either, and maybe there’s a precise definition of fragmentation that I’m not aware of. My understanding is that fragmentation is about software.
The extension scheme allows you to use the same binaries across all platforms. If you care about widespread compatibility, you simply compile-in software emulations of potentially unsupported instructions. If a platform ~does~ support the instructions, the emulation is never used and you get a performance bonus.
> Support for an extension can be checked at runtime, and unsupported instructions can be trapped and emulated.
...isn't that exactly fragmentation?