SQL Server IAM page

Hi Guys, welcome to SQL Server Allocation Series, hope you enjoy the post1 and post2.

Today, I’m going to show you the detail of IAM page.

An Index Allocation Map (IAM) page maps the extents in a 4-GB part of a database file used by an allocation unit. An allocation unit is one of three types:

Holds a partition of a heap or index. LOB_DATA
Holds large object (LOB) data types, such as XML, VARBINARY(max), and VARCHAR(max). ROW_OVERFLOW_DATA
Holds variable length data stored in VARCHAR, NVARCHAR, VARBINARY, or SQL_VARIANT columns that exceed the 8,060 byte row size limit.

Each partition of a heap or