# Database Pages

A page is a fixed-sized block of data

* It can contain tuple, metadata, indexes, log records...
* Most systems do not mix page types
*  Some system require a page to be self-contained

Each page is giving a unique identifier 

* The DBMS uses an indirection layer to map page ids to physical locations

There are 3 different notions of "pages" in the DBMS:

* Hardware page (usually 4KB)
* OS Page (usually 4KB)
* Database Page (512B - 16KB)

By hardware page, we mean at what level device can guarantee a "failsafe write"

![](https://2548495579-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FTsnKOX7xLvOtvOXY9MlI%2Fuploads%2F9q4lPewBzUR4cgBXzMuM%2Fimage.png?alt=media\&token=50b20879-231a-42a9-9dc8-dd996fb0c930)