ELI15: before, when you wrote to disk, you needed a stronger magnetic pulse to change the polarity of the bit. This meant a wider area per bit. Now, we can heat

ELI15: before, when you wrote to disk, you needed a stronger magnetic pulse to change the polarity of the bit. This meant a wider area per bit. Now, we can heat a smaller part of the disk, making it easier to flip the polarity with a smaller magnetic pulse, so the area of the bit doesn't need to be as large, so we can store more info.