Secondary storage is used to protect inactive data written from a primary storage array to a nonvolatile tier of disk, flash or tape. Secondary storage is synonymous with the terms secondary memory, auxiliary storage and external storage.

Secondary storage is a trade-off between high performance and economical long-term archiving. Because it is accessed less frequently, data can be migrated to secondary storage devices with lower performance and costs.

Companies are increasingly placing a second class of storage between primary storage and archival storage as the foundation for a tiered storage environment.

How can I differ secondary storage from a primary storage

Primary memory is the main memory (Hard disk, RAM) where the operating system resides.

Secondary memory can be external devices like CD, floppy magnetic discs etc. secondary storage cannot be directly accessed by the CPU and is also external memory storage.