GATE CS 2009 Q10 — Memory Management and Virtual Memory

To understand what is stored in a page table entry (PTE), let's look at how virtual-to-physical address translation works:

1. Indexing the Page Table: The CPU generates a virtual address consisting of a Virtual Page Number (VPN) and a page offset. The VPN is used directly as an index to locate the corresponding entry in the page table. Since the index itself implicitly represents the VPN, there is no need to store the VPN inside the page table entry. This rules out options A and C.
2. Mapping to Physical Memory: The primary purpose of the page table is to map the virtual page to a physical frame in main memory. Therefore, each page table entry must store the Page Frame Number (PFN). Without the PFN, translation to physical memory is impossible, making it the most essential content.
3. Other Information: While auxiliary bits like access rights (Option D), dirty bits, and valid/invalid bits are often present in a PTE for protection and management, the fundamental and essential translation information is the Page Frame Number.

Thus, the essential content in each entry of a page table is the Page Frame Number.