The word "portable" means a subset of everything possible. Do you think every CPU architecture supports SIMD?
> The word "portable" means a subset of everything possible.
Exactly; for example, C has single precision and double double precision floating point, 64 bit types, and complex arithmetic because every CPU architecture has those built-in.
No, but those things can be easily emulated on every hardware or simply not used. One more reason to use C instead of plain assembly.