> For the complete documentation index, see [llms.txt](https://til.notdu.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://til.notdu.com/database/intro-to-database-systems/buffer-pool-and-memory-management/page-table-vs.-page-directory.md).

# Page Table vs. Page Directory

The page directory is the mapping from page ids to page locations in the database files

-> All changes must be recorded on disk to allow the DBMS to find on restart

The page table is the mapping from page ids to a copy of the page in buffer pool frames 

-> This is an in-memory data structure that does not deed to be stored on disk