Primary Storage has limited capacity and is costly. It cannot preserve data for longer periods. There may be instances where the user needs to store data for a longer duration so that it can be used later. In such scenarios, the secondary storage comes into play. Secondary storage is also called an external memory or an auxiliary storage. The Secondary Storage stores large amounts of .data permanently. This means that the secondary storage is non-volatile in nature. The data remains unaltered even after switching off the computer. Flash memory (e.g. USB drive), CD and DVD drives, floppy disks, magnetic tapes, ZIP drives, punch cards etc. are examples of secondary storage devices.
Secondary storage is not directly attached or connected to the CPU. It is external to the computer and is accessed through input and output channels and, therefore, the time taken by the CPU to access them is more as compared to the primary storage.
Before storing the data, the secondary storage devices need to be formatted based on a file system format as the data is organized into files and directories, providing supplementary information about the data, which is called metadata.
Based primary and secondary storage, there is a third level of storage known as tertiary storage.