I was wondering when copying files is the copy guaranteed to be the same as the original file?

I was just wondering that when copying files could the copies possibly not be the same.

Yes. They're guaranteed to be the same as the original.

Copying files will only not be the same when a cosmic particle hits a bit in your RAM or processor during the copy and your system somehow fails to catch it. Suffice to say, the probability of this is so exceedingly low, I don't believe such an event has ever been verified.

The only other time when a copy is not the same as the original, is when the copy process is interrupted for whatever reason.

In fact, by definition, if the copy is not the same as the original, it's considered damaged or incomplete.

Ok that's reassuring.

what do you mean by a cosmic particle hitting the ram or processor?

A bad copy can be caused by broken RAM, but usually that will cause other problems that you will notice (crashing). A bad CPU would also cause this, but I don't think your PC would be functional enough to even tell it to copy if that was the case.

If you want to check or RAM get yourself a copy of memtest86 and run it for a couple hours. If it shows no errors your RAM is fine.

The cosmic particle thing is where a cosmic ray can hit a transistor in your RAM and cause the stored bit to change. While it is true that this can happen, it is so rare that you can safely ignore it. If you are really paranoid, get yourself a motherboard and RAM that supports ECC.

Ok thanks now I understand.

I use Total Commander's "Synchronize directories - Compare by content" function to be sure files are bit-identical after copying (in rare important cases like copying whole hard disk content to new hard disk, for example).