Memory storage refers to where information is held over time and how it is maintained.

Atkinson–Shiffrin’s (multi-store) model depicts memory as information moving from sensory memory to short-term memory and then to long-term memory. The diagram also emphasizes that unrehearsed information may be lost at early stages, while rehearsal helps keep information active and supports transfer to long-term storage. Source

AP Psychology emphasizes comparing storage systems by duration, capacity, and the type of information (content) they hold.

Big idea: Memory storage systems differ

Across models used in AP Psychology, memory storage is often described as a set of interacting systems. The key comparisons are:

• Duration: how long information remains available

• Capacity: how much can be held at once

• Content: what form the information takes (raw sensation, words, images, meaning)

Sensory memory storage

Sensory memory briefly holds incoming sensory information in its original form, providing continuity between what you sense and what you can attend to.

Duration and capacity

• Duration: extremely brief (typically fractions of a second for vision; a few seconds for audition)

• Capacity: relatively large, because it momentarily registers a wide array of incoming stimuli

Content

• Primarily unprocessed sensory details (e.g., brightness, edges, loudness, pitch)

• Common labels include iconic (visual) and echoic (auditory) storage; the important point is that the information is still close to the original sensation.

Short-term memory (STM) storage

Short-term memory is a limited-capacity, relatively brief storage system that holds information you are consciously using.

A practical way to distinguish STM is that it is defined mainly by limitations.

Duration and capacity

• Duration: brief (often on the order of seconds without active maintenance)

• Capacity: limited; often described as about $7 \pm 2$ items, though real capacity depends on how information is grouped and represented

Content

• Information is often acoustic/phonological (especially for words and numbers), but can also include simple visual information.

• STM content is typically what you can report “right now,” such as a phone number you just looked up.

Working memory storage

Working memory overlaps with STM but emphasizes active manipulation and coordination of information for ongoing tasks (thinking, comprehension, mental maths).

Baddeley and Hitch’s working memory model breaks short-term functioning into specialized components: a central executive that allocates attention, plus sub-systems for verbal information (phonological loop) and visual–spatial information (visuospatial sketchpad). This helps explain why working memory capacity depends on cognitive load and why different kinds of information can interfere with each other differently. Source

Working memory is still “short-term” in duration and capacity, but it is characterized by active processing, not just passive holding.

Duration, capacity, and content

• Duration: brief, moment-to-moment

• Capacity: limited and sensitive to cognitive load (the more you process, the less you can hold)

• Content: information currently being kept available and worked with, such as words being rehearsed mentally or spatial layouts being tracked

Long-term memory (LTM) storage

Long-term memory is the system associated with durable, relatively permanent storage of information over time.

Duration and capacity

• Duration: potentially very long (minutes to decades)

• Capacity: very large (often described as essentially vast in everyday functioning)

Content

LTM stores information in a more meaning-based (semantic) form than sensory memory or STM. Content can include:

• Knowledge (facts, concepts, vocabulary)

• Personal information (people, places, experiences)

• Skills and procedures (how to do things), often stored in a way that supports performance without conscious “holding” in mind

Comparing storage systems by AP categories

A tight AP-aligned comparison focuses on the syllabus phrasing—duration, capacity, content:

• Sensory: shortest duration, high capacity, raw sensory content

• Short-term: short duration, small capacity, immediately conscious content

• Working: short duration, limited capacity, actively processed task-relevant content

• Long-term: longest duration, vast capacity, meaning-based and skill/knowledge content