When I first started using computers, you could buy a 10 megabyte harddrive. "That's amazing!" people of the time exclaimed. "That's like ten really high density floppies!" Last year, I bought a 1 terrabyte harddrive, literally100,000 times the capacity of the first. The larger drive worked pretty much the same way. What changed was the material in the platters, which has been studied continuously to improve the capacity. The newer drives can store more ones and zeros on the same amount of magnetic ribbon. (It also rotates faster, and has a more sophisticated attachment system that transmits the data faster. I could do without this -- I did work for a while completely off live-cds, which are way slower than hard drives, when my big hard drive died.)
So, materials. Typically, you start with chemistry. Is the a more interesting way we can arrange the atoms so that it works better? (Sometimes yes, sometimes no.) In the hard drive's case, we've had to make smaller and smaller magnets, which started with mostly iron, but are now mostly a platinum and chromium alloy.
Mechanics have changed slightly. More plates, smaller magnets, more sophisticated magnet-arm. Not nearly as much as the chemistry.
So...thumbs up for chemistry, even though I suck at it. And that it bears little resemblance to the chemistry most people took in high school or college, with the many tubes of bubbling colored liquid. Making a new material alloy is still chemistry.