Analytic sorts

If you take a 10032 trace you will see that the ROW_NUMBER analytic function uses what is known as a version 1 sort, which is a memory-intensive, insertion-based sort, whereas the FIRST_VALUE function uses a version 2 sort, which is apparently a fancy combination of a radix sort and a quick sort1 that requires much less memory and fewer comparisons.

From Expert Oracle SQL: Optimization, Deployment, and Statistics