in macos 9 it is handled like this: the paths are collected and written into a queue, then the files are copied one by one (as if the user would copy them one by one), and each file is copied from the beginning the the end.
unlike OSX, in which: the paths are collected and written into a queue, then it is made sure that the target volume has enough space, then the files content are copied all at once, and (as far as i can vaguely describe it) the chunks of the content are copied in a random order (i believe the order is based upon what the HD finds the fastest, at least in <10.9/HFS) and when everything is there, the data is finall made files again.
this is why OSX is sometimes 2x faster for copying files and there is virtually no limit of how many files you can copy (while OS9 finder can crash when you copy thousands of files at once)