Historical fiction?

From a conversation at work, the following questions:

What is the difference between "historical fiction" and fiction with a historical setting? And how far back in time do you need to go to be "historical" in this sense? Could fiction written with a modern setting be considered historical fiction in the future?

How do computers work?

Naive question, no?

Seriously, if I'm curious about the on-the-chip workings of a computer, I'm not sure where to even begin finding information. Or even simpler, if I wanted to understand how pre-microprocessor computers worked, where would I even begin? Maybe a kid's electronics kit? "build your own calculator" or something?