"many developers tend to forget that what makes C and C++ usable for systems programming are actually language extensions that are not part of the standard." E

"many developers tend to forget that what makes C and C++ usable for systems programming are actually language extensions that are not part of the standard." Excuse me but what??? Please give an example. Except for maybe setting up an isr vector table and the odd coprocessor command in assembler, all other peripheral functionality is usually memory mapped and perfectly accessible in C and C++.