Plus I think that the 0/1 bits are not encoded as "no magnetism"/"some magnetism", but instead as "north magnetism"/"south magnetism" since magnetic fields have a direction.
And I don't think the magnetic fields on the platters have any appreciable effect on the head besides the electromagnetic effects at the sensor.
Besides that though, the ethos that we have lends itself well to acquiring advanced knowledge in more-or-less all domains, crime and forensics included.