Secondary-Storage Hardware
Main memory, or primary storage, is temporary storage. It works with the CPU chip on the motherboard inside the computer cabinet to hold data and programs for immediate processing. Secondary storage, by contrast, is permanent storage. It is not on the motherboard (although it may still be inside the system cabinet). Secondary storage consists of devices that store data and programs permanently 011 disk or tape.
You may hear people use the term “storage media.” Media refers to the material that stores data, such as disk or magnetic tape. For microcomputers, the principal storage media are diskette (floppy disk), hard disk, magnetic tape, and CD-ROM.
A diskette, or floppy disk, is a removable round, flexible disk that stores data as magnetized spots. The disk is contained in a plastic case to prevent the disk surface from being touched. The most common size is 3.5 inches in diameter.
To use a diskette, you need a disk drive in your computer. A disk drive is a device that holds and spins the diskette inside its case; it “reads” data from and “writes” data to the disk. The words read and write are used a great deal in computing. Read means that the data represented in magnetized spots on the disk (or tape) are converted to electronic signals and transmitted to the memory in the computer. Write means that the electronic information processed by the computer is recorded onto disk (or tape).
If you have been using music CDs (compact disks), you are already familiar with optical disks. An optical disk is a disk that is written and read by lasers. CD-ROM, which stands for compact disk read-only memory, is only one kind of optical-disk format that is used to hold text, graphics, and sound. CD-ROMs can hold hundreds of times more data than diskettes, and can hold more data than many hard disks. A newer type of optical disk called DVD-ROM has more than ten times the capacity of a CD-ROM.