Cianplan

Level 0: Orientation & prerequisites · L0.2 OS & hardware basics for architects

The memory hierarchy

Rank CPU cache, RAM, SSD and network by speed and explain why distance matters.

12 min · Free

What you take away

  • Storage is a ladder: L1 cache ~1 ns, RAM ~100 ns, SSD ~100 µs, same-zone network ~100 µs, cross-region ~60–160 ms.
  • Each rung is roughly 100× slower and much larger than the one above it.
  • You do not choose the rung; the hardware moves data for you, and your access pattern decides how often it wins.
  • Distance is physics: light travels ~30 cm per nanosecond, so a round trip to another continent can never be fast.

How the class is laid out

  1. The problem
  2. The simple version
  3. The ladder
  4. Where the time goes
  5. Check your understanding