Everybody has seen the internals of a hard drive. If you have not, here’s the picture from Wiki
As you can see, the platter looks just like a mirror. Not always..
Recently I got a broken hard drive. A user complained that it produced the sound “like a grinder”. Well, actually it was…
Not bad, eh?
The head fell down and was simply melted on the spindle. The platter was deeply scratched, the mirror-like surface was ground into dust and covered everything inside the drive case.