Why CPUs Need Multiple Cache Levels: A Classic Deep Dive Into the Memory Hierarchy

blaizedsouza · x · 2026-09-07

Fabian Giesen's classic ryg blog post answers why CPUs use multiple cache levels instead of one large L1. The key point: each level faces different constraints—caches grow larger, slower, denser, more power-efficient per bit, and take on more duties as you move up the hierarchy, so no single level can balance latency and capacity. Using an office-worker filing analogy, he builds intuition for cache lines, locality, and per-level trade-offs. A timeless primer on modern CPU memory hierarchies.

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