Data-access operators are used to retrieve data from tables and indexes in SQL Server. Rowstore is the traditional storage mechanism for most Relational Database Management Systems (RDBMS). In a rowstore index, each page of data contains all the columns for one or more rows of data in the table, and so the entire row is stored contiguously across all columns. There are two types of rowstore indexes in SQL Server: clustered and non-clustered. Both index types are stored as a B+Tree data structure, but clustered indexes contain the entire data row at the leaf level, while non-clustered indexes contain only the index columns and a pointer to the data row.
Instead of treating all nodes equal like a B-Tree, the B+Tree structure ...
