Section 5.7: Virtual Memory
For some reason, while there are subsection headers, they didn't put formal subsection numbers in here. So this section has it all! The ideas in this section are very important, so make sure to read it carefully. We care pretty much about all the material in this section.
One of the key concepts to understand (and the main reason virtual memory appears in CS 251) is the TLB (Translation Lookaside Buffer). Basically, it's a cache for the page table.