Lehekülgitabeli

Lehekülgitabel, also known as a page table, is a data structure used by virtual memory management systems to store mappings between virtual addresses and physical addresses. When a program accesses a virtual address, the operating system uses the page table to translate this virtual address into the corresponding physical address in RAM. This process is crucial for allowing programs to use more memory than is physically available, as well as for isolating the memory spaces of different processes.

A page table is typically organized as an array or a tree. Each entry in the page table, called a page table entry (PTE), contains information about a virtual page. This information includes the physical frame number where the virtual page is stored, as well as various status bits. These bits can indicate whether the page is present in memory, whether it has been modified (dirty bit), whether it can be read, written, or executed (protection bits), and whether it has been accessed recently (accessed bit).

When a virtual address is generated by the CPU, it is divided into a virtual page number and an offset within that page. The virtual page number is used as an index into the page table to find the corresponding PTE. If the page is present in memory, the physical frame number from the PTE is combined with the offset to form the physical address. If the page is not in memory, a page fault occurs, and the operating system must retrieve the required page from secondary storage (like a hard drive) and load it into a physical frame before the translation can be completed. The hierarchical structure of page tables, such as multi-level page tables, is often employed to reduce the memory overhead associated with large page tables.