Similar to how in the "POSIX threads" section you indicate that pthread_create() is UNIX/POSIX-specific, you should probably indicate in the "Creating new Processes" section that fork() and execve() are Unix/POSIX-specific. That, or you could indicate that you are describing generally in that context.

In "Running multiple programs" you state: "After a few seconds, it pauses, saves the state of the RAM, and changes processes." Saying it "saves the state of the RAM" is probably not a good characterization since it is more likely just changing what memory is accessible. It is also, most likely changing the virtual memory mappings to give the illusion of using the same memory addresses (though it does not have to, for instance a system with a MPU still has a concept of distinct programs even though virtual memory mappings are not supported), but you could omit that to the later virtual memory section without being incorrect.

Yeah, I purposefully "simplified" how virtual memory works here so that the focus could be on multitasking and context switching, but agree that isn't totally accurate. I actually had hoped to do a part II on virtual memory, but we'll see if time permits that :)

I would like read more about that topics with that level of detail.