Which of these takes the longest?

Options

• ✗ 10,000 reads from main memory
• ✗ Reading 1 MB sequentially from an SSD
• ✗ One disk seek on a spinning hard drive
• ✓ One network round trip from California to Europe Correct

Why

Approximate costs: 10,000 memory reads ≈ 1 ms, 1 MB from an SSD ≈ 1 ms or less, a hard-drive seek ≈ 10 ms, a transatlantic round trip ≈ 150 ms. Distance is bounded by the speed of light in fibre, so no hardware upgrade fixes it.

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