What is this close-up picture? (WotsThat: Hard drive platter surface)

Question

What object is shown in this zoomed-in close-up photo?

VanadiniteX · Accepted Answer

Hard drive platter surface. Hard drive platters are so incredibly smooth that if they were scaled up to the size of Earth, the surface irregularities would be smaller than real mountains and valleys. This extreme smoothness is necessary because the read/write head floats just nanometers above the platter—closer than a human hair is thick—and any dust particle or microscopic bump could cause a catastrophic crash.

Answer: Hard drive platter surface

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