The Knowledge Stack Decoded: Why PKM, RAG, Wikis, and Memory Systems Aren't Interchangeable

These four knowledge management approaches—PKM, RAG, wikis, and AI memory systems—operate at fundamentally different layers and serve distinct purposes, yet they're frequently conflated with serious architectural consequences. Understanding this spectrum is critical for developers and teams: misapplying these systems leads to wikis cluttered with personal scratch notes, RAG pipelines without reliable knowledge sources, and memory layers attempting to function as databases. Properly aligning each system with its intended use case—from personal ideation to collective documentation to machine retrieval to agent persistence—is essential for building effective knowledge infrastructure.