> ## Documentation Index > Fetch the complete documentation index at: https://docs.platform.nora.my/llms.txt > Use this file to discover all available pages before exploring further. # Memory overview > What agents remember — from a single session up to persistent knowledge learned over time. **Memory** is what an Agent remembers on its own — as opposed to **knowledge**, which you author. Memory ranges from very short-lived (a chat session) to very long-lived (facts an Agent has confirmed hold over months). Every Agent can have zero or more **memory spaces** attached. Each space is a container with its own retention, scope, and content model. ## The four space types Notes you or the Agent write, retrievable by keyword or topic. Like a team wiki — human-editable, semi-permanent. Vector-indexed facts. Store any structured or unstructured content; find by similarity. Per-conversation memory. Auto-summarized as conversations grow. Cleared per session by default. Diagnostic memory — patterns that emerged from successful improvements. Read-mostly; auto-populated. See [Memory spaces](/build/memory/spaces) for how to pick. ## Scoping Every memory read and write carries a **scope key**. The same Agent can have separate memory per user, per tenant, per conversation. Different runs never see each other's memory unless you want them to. Scope is a first-class safety property — no accidental leaks across customers. See [Scoping](/build/memory/scoping). ## What lives in memory * Notes (short pieces of text with metadata). * Facts (structured claims about entities). * Relationships between entities. * Procedural rules (behavioral guards). * Session summaries. Every type is retrievable via the same semantic search interface, so an Agent doesn't need to know which kind it's looking for. ## When to use memory vs. knowledge | Use knowledge when... | Use memory when... | | -------------------------------- | ------------------------------------ | | The info is authored and curated | The info is learned from experience | | It changes on your schedule | It changes as the Agent runs | | Everyone sees the same thing | Different users see different things | | Sources are external documents | Sources are the Agent itself | Many Flows use both. Knowledge for reference material; memory for personalization and accumulated context. ## Forgetting Nothing is permanent unless you mark it so. Memory items can be pinned (never forgotten), have TTLs, be superseded (like knowledge), or be pruned by importance decay. See [Forgetting](/build/memory/forgetting).