||SQL Server Tips by Gama and Naughter
Pages and Extents
SQL Server stores data in blocks of 8 Kb called Pages and eight
contiguous extents are the basic unit of storage for tables and
indexes, called Extents. There are two types of extents:
Uniform extents - the entire extent contains data from one table.
Mixed extents - the extent contains data from two to eight different
tables. This is the case of either tables with less than eight pages
or the last pages from a table with a total number of pages multiple
Data Pages are pages that contain data from tables, there are two
ways to organize such pages:
Clustered tables - tables with one clustered index, the pages are
linked in a doubly-linked list using the index as a key and the
index is stored as a B-tree structure. Indexed views have an
identical structure as Clustered tables.
Heaps - tables with no clustered index, the data pages are stored in
no particular order and not linked.
Non-clustered indexes have a B-tree index structure but the data
pages are stored in no particular order.
The above book excerpt is from:
Turbocharge Database Performance with C++ External Procedures
Joseph Gama, P. J. Naughter