There are two main categories of memory: short-term memory and long-term memory.

Short-term memory, also known as working memory, stores information for a brief time and decides whether to discard it or send it to long-term storage.
Long-term memory, on the other hand, holds information for much longer periods. Some long-term memories last a few days, others last for life.

Types of Long-Term Memory

Long-term memory divides into two major types: explicit memory and implicit memory.

Explicit memory is the memory of facts and events. These are memories we can consciously recall.
Implicit memory is unconscious memory. It stores learned skills, habits, and motor patterns, like walking, playing a guitar, or riding a bike. It is built through repetition and practice.

Explicit Memory: Episodic and Semantic

Explicit memory splits further into episodic memory and semantic memory.

  • Episodic memory is memory for experiences and events. It is time-based and personal.
  • Semantic memory is structured knowledge about facts, meanings, and concepts in the world.

Why We Do Not Remember Early Childhood

The key point is that episodic memory does not fully develop until around 3 to 4 years of age.
Before that, babies can recognize faces, voices, and objects (semantic memory) and can learn motor patterns like walking (implicit memory).
But they cannot form lasting, consciously retrievable memories of specific experiences because their episodic memory systems are not yet mature.

That is why you can recognize your parents as a baby and learn how to walk, but you cannot recall those moments later in life. The ability to form true autobiographical memories simply was not online yet.

References

Simply Psychology: Types of Memory
Harvard University: Infantile Amnesia