Disecting a Hard Drive

When I was in 5th grade I dissected a frog. Today we dissected a hard drive.

We found an old 80gb hard drive and decided to turn it into a learning experiment this morning. My girls had never seen a hard drive outside of a computer before and hadn’t particularly thought about what caused the sounds a computer makes when it’s loading something.


We didn’t have exactly the right size torx screwdriver, so we opted for the other method of getting things started.


There was a little manual labor required for getting the case off.



The drive’s head arm was attached to the case firmly. At least until the hacksaw came out.


It required a little more force than expected.



Once the case was off, it was time to inspect the drive and play with its components.


The platter’s surface was perfectly clean and shiny to begin with.



After looking at all the parts, we powered it back up and watched how fast it would spin when the computer booted it up. Of course, by this point there was no virtually chance the drive would be accessible, but it spun up perfectly and the read/write head moved back enough times to provide a good show.


We noticed a few things:

  • The read/write head is amazingly close to the surface of the platter without touching. We quickly scratched up the platter with our fingers playing with the drive, but even after touching the head, it never “crashed” into the surface of the drive’s platter or scratched it. The tolerances are amazingly fine.
  • The platter is a super smooth surface and the bearings make it spin incredibly smoothly. It’s pretty fun to spin by hand because it goes for a while.
  • This drive has a lock that you have to press lightly to allow the read/write head to move. I assume this protects the drive by helping to ensure the read/write head doesn’t crash into the platter in the case of a drop.
  • I was surprised my girls made the connection between the platter in a hard drive and the record. I didn’t know they’d ever seen a record player.
  • The difference in diameter between the inside of the platter and the outside of the platter is really significant. With a little explaining that the drive spins at a constant rate (this one at 3600 RPM) our 10 year old was able to understand that you’d want to put the data you want fastest near the outside of the platter. I knew this concept, but I had never realized the size difference until I had one in my hand.
  • This is going to be a lot less interesting in a few years when we only have SSD drives to dissect.
  • Overall, a fun experiment for all of us this morning.
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