Why the progress bar of copiers don't work as they should?

Question

Don't you ever haved a copy task and saw that the progress bar just stoped and continue after a while? The function of a progress bar shoul be that it's increment must be uniform for having a better idea of what time the copy will last. Simple question...

Answer 1

uxcuse me:
Do you need answare for program lenguage, or for a action to copy (files in pc)?