Heap Tables
A table without a clustered index is a heap table. There is no imposed ordering of the data rows for a heap table. Additionally, there is no direct linkage between the pages in a heap table.
By default, a heap has a single partition. Heaps have one row in sys.partitions, with an index ID of 0 for each partition used by the heap. When a heap has multiple partitions, each partition has a heap structure that contains the data for that specific partition. For example, if a heap has four partitions, there are four heap structures (one in each partition) and four rows in sys.partitions.
Depending on the data types in the heap, each heap structure has one or more allocation units to store and manage the data for each partition. At a minimum, ...
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