Page Table

Definition

A page table is a data structure used by the operating system to manage virtual memory. It maps virtual addresses to physical addresses, allowing the system to retrieve data from memory efficiently. This structure plays a crucial role in implementing virtual memory through paging, which divides the memory into fixed-size blocks called pages. Additionally, it enhances the memory hierarchy by providing an organized way to handle locality of reference, optimizing memory access patterns and performance.

5 Must Know Facts For Your Next Test

1. Each entry in a page table contains the frame number where the corresponding page is stored in physical memory, along with status bits indicating whether the page is in memory or has been swapped out.
2. Page tables can vary in size depending on the architecture and amount of virtual memory used, leading to possible performance issues if they become too large.
3. Some systems implement hierarchical page tables or inverted page tables to manage large address spaces more efficiently.
4. The operating system can use page tables to implement demand paging, which loads pages into physical memory only when they are needed, saving resources.
5. When a page fault occurs, the operating system must access the page table to determine where the required page is located and then bring it into physical memory from secondary storage.

Review Questions

• How does a page table facilitate efficient memory management in a virtual memory system?
  • A page table facilitates efficient memory management by providing a mapping between virtual addresses and physical addresses, allowing processes to access memory without needing contiguous physical space. When a program requests data using a virtual address, the system consults the page table to find the corresponding physical address. This mapping allows for optimal use of available memory and supports features like paging and demand paging, which together enhance performance and flexibility in managing memory resources.
• Evaluate the impact of page tables on system performance and locality of reference.
  • Page tables significantly impact system performance by directly affecting how quickly data can be accessed in memory. The organization of virtual addresses into pages allows for better exploitation of locality of reference since programs often access data and instructions that are close together. However, if page tables are too large or inefficiently managed, they can lead to increased overhead during address translation. Therefore, maintaining an effective page table structure is crucial for optimizing both speed and resource usage.
• Critically analyze how hierarchical page tables differ from traditional flat page tables and their implications for large address spaces.
  • Hierarchical page tables divide the page table into multiple levels, reducing the amount of memory needed to store mappings for processes with sparse address spaces. In contrast, traditional flat page tables require contiguous storage for all potential mappings, which can be inefficient for systems with large but sparsely used address spaces. By using a hierarchical approach, systems can significantly lower memory consumption for storing page table entries while still enabling quick access to necessary mappings. This method is especially beneficial as it scales better with larger virtual address spaces found in modern applications.

Related terms

Paging: A memory management scheme that eliminates the need for contiguous allocation of physical memory and allows the physical address space of a process to be noncontiguous.

Segmentation: A memory management technique that divides the process's address space into segments of various lengths, representing logical units such as functions or data structures.

TLB (Translation Lookaside Buffer): A special cache that stores recent translations of virtual memory addresses to physical addresses, speeding up the address translation process.