That depends on the particular counter, and the features you’ve enabled.
Every banknote counter can count sorted notes using an optical sensor that tallies bills as they pass by, but to count mixed notes—a stack of bills that contains ones, fives, tens, and twenties, say—the device must be able to recognize the different denominations while it counts. (All the bills do have to be the same currency.) Advanced counters like the LD-2100 and LD-2040 and so on can tally up every denomination in the stack in a single pass, which saves a huge amount of time compared to sorting the bills first yourself.
