Three systems with different capacities and timescales
Sensory memory holds unprocessed information from the senses for a very brief window (under 1 second for vision, a few seconds for sound). It captures rich detail but decays rapidly unless attended. Short-term or working memory holds about 4-7 chunks and lasts roughly 30 seconds without rehearsal, enabling you to hold a phone number in mind while dialing.
Long-term memory is the permanent store, holding information across years or a lifetime. The bottleneck between these systems is encoding: getting information from sensory input into working memory and then consolidating it into long-term storage requires attention and active processing. Information that bypasses this process (like the precise layout of a familiar room you never consciously studied) is often forgotten rapidly.
Rehearsal, encoding, and retrieval
Maintenance rehearsal (repeating a phone number to keep it in working memory) extends short-term retention but does little for long-term storage. Elaborative rehearsal (linking new information to existing knowledge) drives consolidation into long-term memory. Studying the same material multiple times spaced over days is far more effective than cramming, because spaced retrieval forces the brain to reconstruct memories, strengthening them.
Retrieval cues determine what you can recall. A familiar context, a related thought, or a partial cue can trigger recall of forgotten information. This is why recognition tests (pick the right answer from options) are easier than recall (generate the answer from nothing), and why you remember more in the room where you learned something. Understanding these principles allows more efficient learning and better strategies for retaining important information.