Primary memory is the internal working memory of a computer, and it includes RAM and the cache.
Secondary storage is also called external memory, and it includes the computer’s hard drive.
Primary storage is the fastest memory in the computer, but it only holds information for a short period of time while the computer is running. The data from primary storage tends to go away after the computer is turned off. When a user activates a program on a computer, data is moved from secondary storage devices into the RAM and cache of primary storage in order for the computer to actually use it. Secondary storage includes a CD-RW, a USB thumb drive, a tape drive, a floppy disk or anything else that is not used for the computer’s main memory.
Offline storage is storage which is swapped out by a user - that includes hot swap hard drives and flash drives (if being swapped out frequently by a human operator), CDs, blu-ray disks