select count(1) from table versus select count(1) from table partition

Hello

I am comparing the explain plan for the two selects

select count(1) fromTABLE  partition (P_CURRENT);

and

select count(1) from TABLE

I noticed that in the first case explain plan shows INDEX FULL SCAN and in the second case explain plan shows INDEX FAST FULL SCAN. There are no difference in the explain plans besides that step

The second query finishes significantly faster than the first one (.25s versus 2+s ). Both queries use the same index  which is nonunique and nonpartitioned.

Can someone suggest what could be  the reason for the difference in the explain plan?

Thank you