Secondary storage devices consist of media like CDs or DVDs, or physical devices, such as flash memory drives or external hard drives. Older computer systems also used floppy disks or magnetic tapes for secondary storage.
Secondary storage is used as a cheaper alternative to internal hard drives, and differs from components like a computer's RAM memory by being a permanent storage medium. A computer cannot directly manipulate the data on a secondary storage device without RAM to store and run the data; information is instead quickly read into memory to be written back onto the device. In the case of media that cannot be written to multiple times, data on the hard drive refers to resources on the disc, and both are used to run software while saving the results.