What does "preparing for copy" do?
"Preparing to copy" is a special feature that allows to delay the whole process by unreasonable amount of time and gives you more time to appreciate a fancy dialogue box created by Microsoft designers.
While windows is "preparing to copy" it does not
- Check for possibly locked files (those will only be revealed during actual copying process, for obvious reasons)
- Make any changes to your file system (also note that actual filesystem is not the factor here, behavior is the same for NTFS / FAT32)
What it does though is creating the full list of files and performing some magic number calculations to make wrong assumptions about estimated copy time.
It builds the list of all files in the current folder and its subfolders and logs the changes that will be made to the files in a journal. That's necessary because of the way that NTFS works.
Some use cases of that list include:
- updating file system
- maintaining file consistency in case of a failure
- knowing the number of files so you can compute how much time is left to complete the operation, what percentage of the operation has been completed so far and draw the progress bar accordingly.
- providing user to retry or abort the operation (whether it's copy, move, delete) when it fails on some file(s).
If that's annoying you can always use xcopy or robocopy via command prompt for large number of file operations.
As answered by Raymond Chen in one of the replies to his original File copy progress dialog post (http://blogs.msdn.com/b/oldnewthing/archive/2004/01/06/47937.aspx#47964), one of the things it does is to get the filesizes for the entire copy operation to make a better guesstimate about the time the copy will take.
I believe this fancy feature is to calculate the progress bar percentage when each file is copied, so that you can appreciate the lovely progress bar.