Introduction to Computer Systems has a more scientific or technical content than most introductory texts in Computer Science. The reason is that the physical and logical principles are much longer lived than the specifics of computer hardware and software, which change very rapidly. A description of how something works is better than a superficial picture of the hardware. It's better because knowing the principles opens to door to making associations and links to other knowledge, and making those links are what is meant by understanding. To learn how the primary memory of a computer works is better than merely seeing pictures of little circuit boards that we use for the primary memory.
Most introductory texts say that data is transferred inside the computer, e.g., between the memory and the main processor. But what physically happens to cause the data to move from point A to point B? Knowledge more firmly linked to basic principles has greater value. Experience over the last 10 years has shown that student interest perks up when a few concrete examples or analogies show how a computer works. Being too general or abstract is not the way to stimulate interest or establish a proper foundation for later studies and professional life.