Why is the time remaining so wrong?

Question

I've noticed over the past few years that the "Time Remaining" estimates from various applications in OS X are increasingly inaccurate - usually the estimate is too long!
This is true for apps from Itunes, to Disk Utility, to <on and on and on>. For example, I was just burning a DVD from a playlist in ITunes and when it started the "Finishing" part - it said "Might be up to an hour". It completed in 30 seconds.
Time estimates are just that - estimates - but do they have to be so wildly inaccurate as to be useless as a guide? I have a feeling nobody in the OS X world has looked at how they update the estimate in a long time, and they do not presently reflect the performance of either hardware or software.
Hey Apple!  Update the Time Remaining code! Please?
David

Answer 1

Ignoring the boot progress bar (which I believe is an animation, at least it was in my old Tiger system), the progress bars are usually computed by specifying a range of values to produce a scaling factor and updated by supplying values within that range.  The amount of progress is determined by the supplied values within the range.
The segment of code responsible for supplying values is given control on some criteria within the algorithm doing whatever the progress is to measure.  There's potentially a lot of variables that can affect when this segment of code is called to update its progress.  With disk copies there's how fast the drives are, buffer sizes, what else is running that could interrupt the process, and who knows what else.  Certainly you should not expect the progress bar drawing to have a high priority in the grand scheme of things.  I'd rather the service be "obsessed" with its primary goal (whatever its service is to do) rather then keeping me constantly updated every millisecond taking valuable cycles from the primary task.