Common terms

Pages

• fundamental unit of data storage in SQL Server is the page
• The disk space allocated to a data file (.mdf or .ndf) in a database is logically divided into pages numbered contiguously from 0 to n. Disk I/O operations are performed at the page level. That is, SQL Server reads or writes whole data pages.

Extents
Extents are a collection of eight physically contiguous pages and are used to efficiently manage the pages. All pages are stored in extents.