I know roughly how hard-drives work; that the hard-drive involves multiple platters and multiple heads. A platter is a disk coated with some magnetic material and capable of being spun at high RPM. The drive-head has the capability to change the domain orientation on each magnetic dot to register as a 0/1.
What has me flummoxed is that adjacent drives are kept so close together without deleterious effect. Is the field strength so weak that it has no impact on it's adjacent platter? If not, how is the interference of adjacent platters cancelled?