It is now. There were more esoteric platforms for which it was defined as 2 bytes (eg csr8675 and the Kalimba DSP coprocessor was even 24-bit char, short and ints). Until recently C only defined that char was the smallest unit and had size 1. I think as of C11 that may have changed. It definitely did in C++ because basically any platform that mattered defined char as 1 byte and any platforms that didn’t also didn’t really care about portability of existing software that much as the porting is generally more involved anyway (eg I ported a crypto library to Kalimba and it was challenging to get the bit math correct but eventually I did).