Just to get a little more specific with this: the shift is in the accepted "main engine of computation" (to make up a mediocre term). We used to have somethin

Just to get a little more specific with this: the shift is in the accepted "main engine of computation" (to make up a mediocre term). We used to have something of an engineer's viewpoint, that the physical location of the electrical operation of the mathematics (i.e., the CPU) was this main engine. It's been a long road, but the new viewpoint is a bit more philosophical: the main engine is the human-computer nexus. Of course, "human" in the above isn't strictly correct, since we know that computers talk to each other all the time, too. Indeed, when that happens the main engine of computation isn't really one or the other of the computers, but the link between them (i.e., the protocol). So now "blocking" means requiring the main engine of computation to "sleep" and wait for "external input". For a human UI this means the classic sense of waiting on the wetware end, but it can just as easily mean waiting on the hardware end. We strive to build responsive systems, so we wish for them to be "non-blocking" in every case. This means, if the human wants to communicate to the computer, it shouldn't be prevented to because the computer is currently working on a solitary operation. Ultimately it's the same principle we've already accepted from the reverse direction.