Here's an interesting quote I came across this evening while reading the introduction of the online course Building a Modern Computer From First Principles:

It turns out that this strategy works well thanks to a special gift unique to humans: our ability to create and use abstractions. The notion of abstraction, central to many arts and sciences, is normally taken to be a mental expression that seeks to separate in thought, and capture in some concise manner, the essence of some entity. In computer science, we take the notion of abstraction very concretely, defining it to be a statement of "what the entity does" and ignoring the details of "how it does it." This functional description must capture all that needs to be known in order to use the entity's services, and nothing more. All the work, cleverness, information, and drama that went into the entity's implementation are concealed from the client who is supposed to use it, since they are simply irrelevant. The articulation, use, and implementation of such abstractions are the bread and butter of our professional practice: Every hardware and software developer is routinely defining abstractions (also called "interfaces") and then implementing them, or asking other people to implement them. The abstractions are often built layer upon layer, resulting in higher and higher levels of capabilities.

The site contains all the software tools and project materials necessary to build a general-purpose computer system from the ground up, so check it out if you dare to take up this amazing challenge.