The work done by a computer would be useless if it were to disappear at the end of the work session. Yet that is exactly what would happen in most computers if the work was left in RAM, the machine s temporary memory. RAM is designed to accommodate the task at hand, but is operational only so long as the power is switched on. The instant the power goes off, whether by accident or design, RAM is once more an empty slate. To use and re-use programs and files from session to session, the user must save a newly created or freshly updated document to storage, an electronic filing system that will keep its contents in order, even with the power off.
Modern computers make use of two storage technologies - magnetic and optical.
Data storage methods relying on magnetism have predominated through most of electronic computing history with optical technology only coming on the scene in the 1970s. Tape was an early magnetic medium which continues to be used widely for backup and for archival storage of data. Borrowed from the music recording industry, tape a great leap forward. In 1971, IBM introduced the considerably smaller, flexible magnetic disk, the now commonplace floppy. Since their debuts, both hard and floppy disks have shrunk steadily in size and just as steadily grown in capacity.