Thank you so much for your valuable info, Data Doctor.
I'd like to ask one question that still puzzles in my mind.
If hard disk has errors due to improper shutdown or many times reset, then can we recover data efficiently?
Yeah, my hard disc has a lot of such errors.
When I recover data using ONTrack Data Recovery software, my hard disc sounds bad "#@#@$@". The process is slower than the hard disc with no flaws.