Hi, I know there is this question already discussed, but I still don´t understand something, so please just help me clarify it.

What I understand there is 2 way to do I/O aka communicate from CPU with other HW. One is to use in and out instructions, and second is the memory mapped.

But what I don´t actually understand is, is IN and OUT instructions are used, you define source port. But what is this port? I mean, is it different set of pins on CPU or what? And, to what is that port connected?

And for the memory mapped, I miss just a tiny detail. Wheather memory mapped I/O must be first set by IN and OUT instructions, or does the device actually somehow itself connects to the RAM and reads it? Thanks.