Direct links to this section: Primary storage, Main memory, Internal Memory.
Secondary storage (or external memory) differs from primary storage in that it is not directly accessible by the CPU
Tape cartridges placed on shelves in the front, robotic arm moving in the back. Visible height of the library is about 180 cm.
Tertiary storage or tertiary memory, provides a third level of storage. Typically it involves a robotic mechanism which will mount (insert) and dismount removable mass storage media into a storage device according to the system's demands; this data is often copied to secondary storage before use Off-line storage
Off-line storage is a computer data storage on a medium or a device that is not under the control of a processing unit. The medium is recorded, usually in a secondary or tertiary storage device, and then physically removed or disconnected. It must be inserted or connected by a human operator before a computer can access it again. Unlike tertiary storage, it cannot be accessed without human interaction.