Each "type" of memory has specific structures/characteristics. The characteristics of memory determine what can be stored. So the question; "What is being stored in memory", may be best answered by describing the "types" of human memory. The next section will discuss this.
Sensory memory(SM) is affiliated with the transduction of energy (change from one energy from to another). The environment makes available a variety of sources of information (light, sound, smell, heat, cold, etc.), but the brain only understands electrical energy. The body has special sensory receptor cells that transduce (change from one form of energy to another) this external energy to something the brain can understand. In the process of transduction, a memory is created. This memory is very short (less than 1/2 second for vision; about 3 seconds for hearing). A sensory memory exists for each sensory channel: iconic memory for visual stimuli, echoic memory for aural stimuli and haptic memory for touch.
Working Memory (WM) is assumed to consist of a limited pool of processing resources that can be allocated to different tasks either consciously or unconsciously.
If something important enters the SM, working memory resources can be allocated to paying attention to that incoming information. That, of course, leaves fewer resources for any other task. Chunking, i.e. combining and processing related bits of information together can lead to an increase in the WM's capacity. (Miller 1956).
Besides paying attention to new information, working memory resources could also be allocated to encoding/storing information into Long-Term Memory as one does when trying to remember someone's name or an important piece of information perhaps for some future test. Due to the limitations of the WM one cannot do too many things at the same time if one hopes to do any of them well. .
Long-term memory (LTM) is also called preconscious and unconscious memory in Freudian terms.
