Summary

Secondary storage in computer systems refers to a type of storage used to hold data and programs that are not actively being used by the computer's central processing unit (CPU). 

Unlike the computer's primary memory (RAM), which is volatile and loses its content when the computer is turned off, secondary storage is non-volatile, meaning it retains data even when the power is off. 

Examples of secondary storage devices are hard disk drives (HDDs) and solid-state drives (SSDs). Secondary storage is essential because it allows users to store large amounts of data permanently, like documents, photos, and software, ensuring they are not lost when the computer is shut down. This extra storage space is crucial for accommodating data that cannot fit in the limited and temporary memory of the computer's RAM.