I was very surprised to learn that there are actually three types of memory. According to Multimodal Learning Through Media: What the Research Says, these are: working memory, sensory memory, and long-term memory.
Working memory is where thinking gets done. It is dual coded with a buffer for storage of verbal/text elements and a second buffer for visual/spatial elements. Working memory is short-term and limited to approximately four objects that can be simultaneously stored in visual/spatial memory and approximately seven objects that can be simultaneously stored in verbal short-term memory. [Keep in mind that these ‘objects’ could be very large and complex schemas.]
If the person shifts attention when those buffers are full, new elements may be introduced … Read the rest