Know It All

  How does a hard drive store so much information in such a small space? At the heart of every hard drive is a stack of high-speed spinning discs with a recording head flying over each surface. Each disc is coated with a film of microscopic magnetised metal grains, and our data doesn't live there in a form you can recognize. Instead, it is recorded as a magnetic pattern formed by groups of those tiny grains. In each group also known as a bit, all of the grains have their magnetizations aligned in one of the two possible states, which corresponds to zeros and ones. Data is written onto the disc by converting strings of bits into electrical current fed through an electromagnet. This magnet generates a field strong enough to change the direction of the metal grain's magnetization. Once this information is written onto the disc,  the drive uses a magnetic reader to turn it back into a useful form, which is much like a phonograph needle.  But how can you get so much of information o