Low-level programming cares a lot about data layout. It's a big deal. It also pervasively influences the rest of the language, so we're going to start by digging into how data is represented in Rust.
This chapter is ideally in agreement with, and rendered redundant by, the Type Layout section of the Reference. When this book was first written, the reference was in complete disrepair, and the Rustonomicon was attempting to serve as a partial replacement for the reference. This is no longer the case, so this whole chapter can ideally be deleted.
We'll keep this chapter around for a bit longer, but ideally you should be contributing any new facts or improvements to the Reference instead.