You may be wondering what is this magic number 900 rows within a batch? Well, when executing a query in BatchMode, SQL Server allocates a 64k bytes structure to group the rows. The number of rows in this structure can vary between 64 to 900 depending upon number of columns selected. For the example above, there are two columns that are referenced and X marks the rows that qualified in the BatchMode structure shown in the picture below. If SCAN is part of a bigger query execution tree, the pointer to this structure is passed to the next operator for further processing. Not all operators can be executed in BatchMode. Please refer to Industry leading analtyics query performance for details on BatchMode Operators.
Under the right circumstances, BatchMode execution can be a major performance benefit.