Top N and SET rowcount n which is faster?

Lazy to translate, to the effect:
Top N and SET rowcount n are as fast when there is an appropriate index. But for a unordered heap, top n is faster.
Principle to see English.
Q. are using the top N clause faster than using SET rowcount N to return a specific number of rows from query?
A. With proper indexes, the top n clause and SET rowcount n statement are equally fast, but with unsorted input from a hea P, top N is faster. With unsorted input, the top N operator uses a small internal sorted temporary table in which it replaces ' last RO W. If the The input is nearly sorted, the top N engine must delete or insert the last row of a few times. Nearly sorted means ' re dealing with a heap with ordered inserts for the initial population and without many, D Eletes, forwarding pointers, and so on afterward.
A nearly sorted heap is more efficient to sort than sorting a huge table. In a test so used top N to sort a table with the same number of rows but with unordered inserts, Top n is not as Effici ENT anymore. Usually, the I/O same both with a index and without; However, without a index SQL Server must do a complete table scan. Processor time and elapsed the efficiency of the nearly sorted heap. The I/O time are the same because SQL Server must read all the rows either way.