They say that people don't change. I'm not so sure about that. Don't compromise: it seems so simple. You have to let the mind wander.
You get the memory bus and the peripheral bus, but then you get what's memory-mapped, and wonder why everything isn't. And it's better to look at it as if there is only one bus (the old days, in this circumstance, refers to attempts to make things ideally). Now we have what's multiprocessor (asymmetric if you like); uninitialized variables disappear and we land up with what changes while we're reading.
Agreements then need to be put in place, and the imagination suggests giving a pair of variables an owner each.
Then we come to what, in some systems, is called a programmable interrupt controller. It's generally expected a peripheral is monitoring writes, so this is a one way signal. Now we come to what's called expensive, because to respond to an interrupt request, which we had learnt to say eye-argh-queue for, involves entering unprotected mode (or leaving protected mode, but I ask you to tell me that's better), which, we weren't allowed to forget, is expensive. Very.
Fortunately we have an actual fantastical machine represented by what dry-runs.
My stomach is in knots about wheelchairs. Enjoyment of what's beneath the stars isn't something we can get away with, without getting some stellar people up in arms.
But I suppose we are the changing people, though I speak with none but my own explicit consent to call us that.
A sex change? I wouldn't want to know the turmoil of that kind of stomach.