The number of rows stored on a page depends on the size of each row. For a table that has all fixed-length, non-nullable columns, the size of the row and the number of rows that can be stored on a page are always the same. If the table has any variable or nullable fields, the number of rows stored on the page depends on the size of each row. SQL Server attempts to fit as many rows as possible in a page. Smaller row sizes allow SQL Server to fit more rows on a page, which reduces page I/O and allows more data pages to fit in memory. This helps improve system performance by reducing the number of times SQL Server has to read data in from disk.
Impact of row and page size on performance in terms of I/O cost
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