What real platforms map hardware ports to memory addresses?

Question

I sometimes see statements that on some platforms the following C or C++ code:

int* ptr;
*ptr = 0;

can result in writing to a hardware input-ou

Answer 1

This is called Memory-mapped I/O, and a good place to start is the Wikipedia article.

Modern operating systems usually protect you from this unless you're writing drivers, but this technique is relevant even on PC architectures. Remember the DOS 640Kb limit? That's because memory addresses from 640K to 1Mb were allocated for I/O.