[mkup]

The difference between modern days and days of DOS isn't in C/C++ compiler, it's in virtual memory and address space isolation and privilege isolation. So it's not a job of a C/C++ compiler to enforce protection from writing to "special" addresses, because interrupt table updates (and memory-mapped hardware I/O in general) still must happen somewhere (i.e. in kernel, hypervisor, drivers etc) and that code is still written in C/C++, same as in the DOS era.

[sargstuff]

Mmmm..;. job of modern OS is to use/manage MMU. Prior to DEC, OS just automated version of human feeding punch cards/spooling up tape.

DEC provided the necessary hardware MMU to do actual real time multi-processing/multi-user access in feasibile/practical manner.