Files in filemanager Module

Hi,

can anyone tell me why the filemanager module stores the attached files (i am using filemanager.module + attachment.module) of a node in active/0/ || active/1/ || active/2 ???

Why three directories? When does the module stores the file in /0 /1 or /2? Is there any difference between files?

I'll hope someone can tell me.... otherwise i'll have to read many code.

Greetings,

Jott