Very closely connected to the processor. Used to hold the programs and data that the processor is actively working with. The processor interacts with it millions of times per second. The contents of main memory is easily changed. Not used for long-term storage.
Low capacity compared to secondary memory, but access is fast.
Connected to main memory. Used to hold programs and data. The processor does not interact directly with secondary memory. When programs and data become active, they are copied from secondary memory into main memory where the processor can interact with them. A copy remains in secondary memory The contents of secondary storage is easily changed.