FORCE_DISK causes the query engine to use disk instead of memory for temporary storage of the data required to process the ORDER BY operator. This frees up memory for other server operations. FORCE_DISK is useful for queries that consume a large amount of memory and affect performance of other processes running on the server.

If FORCE_DISK is not specified, the query engine uses memory instead of disk, whenever possible, to speed performance.

This ORDER BY option takes precedence over the SELECT-level FORCE_DISK option.