When you tell your Mac to save a file, your Mac's logic board sends signals to the hard drive's controller circuitry. However, data isn't always written to one contiguous space. The drive controller saves incoming data to any unoccupied space it finds. If, while writing a file it fills one space, it moves to the next available area and puts the rest of the file there. The smallest fingerprint is an impassable mountain.
All air going into the case passes through filters that trap damaging debris molecules.
We rarely think about our hard drives, but they're always in the background, saving and serving up our data. For all the demand we place on them, their abilities are amazing.