Final answer:
The essential content of a page table entry is the Page frame number, which maps virtual addresses to physical memory locations. Access rights information is also present, but the virtual page number is implied by the entry's index in the table.
Step-by-step explanation:
The essential content in each entry of a page table is the Page frame number. The page table is a data structure used by a computer's virtual memory system to store the mapping between virtual addresses and physical addresses. When a program accesses a virtual address, the page table entry (PTE) for the corresponding virtual page number contains the physical page frame number where the actual data resides, along with other information like access rights information. However, the virtual page number is typically not stored in the PTE because the index of the entry within the page table implicitly represents the virtual page number.