Primary memory, also known as working memory, was first named in the 1960's but discovered earlier. It is considered the brain's short term memory storage and is likened to computer storage memory.
Primary memory is used to hold onto current information that the brain needs to figure out complex problems that involve reasoning and learning. Anything that needs attention involves primary or working memory.
Characteristics of working memory include holding onto small amounts of information at one time, a few bits of information that is needed to complete the current task. This is because the working memory is used for learning new information and therefore holds only a small amount in storage.
Also, when used in conjunction with long term memory, the ability of the working memory to hold more information becomes greater.
Working memory is also short in duration. It takes effort to hold onto working memory because it is used only to store current and relevant information to completing a current task only.
There continues to be more research done in this field to gain a better understanding of how the brain works to process information and how it stores what is learned.
I hope this helped,