It is not difficult to imagine the differences in mechanics between a CD player and a hard drive. A CD player uses a laser to bounce a tiny beam of light off a spinning polycarbonate disc with a silvered layer of metal that contains slight depressions on its surface. The reflected light is received by a sensor that can differentiate between the valleys and peaks moulded into the surface and reflected back to the sensor for reading by a thin layer of aluminum. This mechanism is also required to perform the same duties with a different process for CDRs. Instead of peaks and valleys molded into the plastic surface of the disc, burn marks from a recording laser create differences in contrast between themselves and the virgin areas next to it. A hard drive does something very different. Instead of a plastic moulded disc, hard disc drives uses metal discs polished to a flatness specification of one Angstrom unit, a measurement of light about the size of an atom. Without ever making contact with the metal disc, a magnetic head flies across the spinning polished disc to read tiny patches of magnetic materials beneath it; a modern day version of a tape recorder.
Each of these devices has the same goal: to read data stored on their medium. The data may be identical, but the process of reading that data is as different as white is to black.
And given the very different nature of each mechanism, why would successfully retrieving identical data make a sonic difference? We'll start to dig deeper.
