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records, but instead of grooves, small magnetic blocks are used to save or load information in the form of 0's and 1's by magnetizing or reading the magnetized polarity on the platter's surface. They also have a 'head', that like a record player, swing to and fro over the platters to read or write information.
This is an amazing piece of robotics but it has it's limits… Although hard-drives come installed in laptops, they are not really intended to be used whilst moving. A small bump can cause the head to bump against the platter, causing irreparable damage. Hard-drives can recover and ignore that 'bad block' but over time the disk will quickly continue to degrade, until eventually one day, your data is lost.