What’s the difference between Hard Disk Drives (HDD) and Solid State Drives (SSD)?
Platters with the ability to store data magnetically in concentric circles (tracks) are spun by a spindle motor. A “head” on the end of an “arm” is used to read/write data on these “tracks”. This arm is attached to an actuator, or stepper motor for older hard drives, which moves the head to the track to be read or written.
Hard disk drives mechanical ability and incredibly high tolerances are amazing. The spindle motor in common HDDs spins at 5400 or 7200 revolutions per minute (RPM), with higher end server drives up to 15,000 RPM.
While the platters are spinning, the read/write head is flying over them at 3 nanometers (billionths of a meter). At this height, a dust or smoke particle can collide with the head and disrupt operation. Due to this, the head/disk assembly (HDA) of the HDD is sealed in a clean room to avoid contaminants.
Since the head needs an “air bearing” to fly over, the HDA is usually ventilated with a filter to equalize pressure, while barring the finest particulate matter. Specifically because of the need for this air bearing, unpressurized, high altitude applications are an issue for HDD.