Answer from cs61c-em (JinHyung Park 17762465) for Question 1
The processor generates virtual addresses while the memory is accessed using physical addresses. Both the virtual memory and the physical memory are broken into pages, so that a virtual page is really mapped to a physical page. It is also possible for a virtual page to be absent from main memory and not be mapped to a physical address, residing instead on disk. Physical pages can be shared by having two virtual addresses point to the same physical address. This capability is used to allow two different programs to share data or code.