Wheareas our Lond term memory is almost infinite in capacity, our working memory can only handle a few items in the same time. For instance, if we are about to give a telephone call, and have just read the number to call, we'd better repeat the series of numbers aloud, since they could rapidly be forgotten. This is due to our limitations in short term memory as Miller has demonstrated.

Our short term memory is also our working memory that not only handles the contents (initial numbers for example) but also the operations (division for example) and temporary results (carry for example). Rapidly, we have to help ourselves by writing down (written division) all those elements since our memory capacity is limited.

Fortunately, working memory and chunking help cope with the complexity.