I am going through a cleanup and I had chosen to delete the Windows.old files.
I heard that they would be deleted in 30 days anyway through other literature that I had read. But I bit the bullet because everything looked okay with Windows 10 and decided to include the Windows.old files within CC Cleaners routine.
It has been 2 days and it is still at 42%. It is moving still... but still moving albeit verrrrry slow...lol.
I realize that 32 passes takes longer... how much longer should I expect to wait for this thing to get done. Because I should probably restart my computer at some point...lol.
Multiple passes are useless, and it's faster and better to let the windows cleanup utility to clean the windows old folder as I think win10 may have locked some files in it.
Also the windows old folder is about 2-4 GB in size. 35 passes is the equivalent of writing 70-140GB of data; it seems, to me that one can safely assume this would both take a long time and cause some pretty extreme wear on your harddrive making it likely that your drive will die much sooner than it would have before you began the removal.
I feel that it's best to expand a bit about window locking some of those files in the windows.old folder.
First of all it is a theory based on a small sample size (total universe of a single PC), so I may well be wrong.
After my update I was 100% sure that, though i liked and had no issues with the older OS, I would not be rolling back to windows 8.1. While I don't know if the windows.old folder is related to the rollback in any way, I knew I had a huge folder sitting there that I didn't need. I attempted to manually delete it and it hung on a "cannot remove file in use" warning. I then found the disc cleanup tool (note: it's been moved from where it was in previous windows) enabled Administrator cleanup and checked off the enable "old windows versions" mark (not verbatim). It took about ten-to-twenty-five minutes.
Hope this link assists regarding "windows old" folder, how to delete, why is it there and: But, don’t wait too long — Windows will automatically delete the Windows.old folder to free up space after a month. (from the howtogeek article)