Also C was designed for PDP-7/PDP-11 style machines with 8-bit bytes, 16-bit words and the like. It was ported to a variety of other architectures which had to make assumptions and adaptations. These live in UB.

One somewhat unfortunate side effect of the pervasiveness of C and Unix-style machines is that it encouraged CPUs to optimize for C rather than the opposite way around. The use of GPUs for non-graphics programming is a welcome improvement.