Storage Media

The term "storage media" can refer to several different things. It can be the objects on which data is stored, or the cables linking systems together in a computer network, or the form used to communicate information such as pictures or video.

The earliest form of mass storage dates back to the turn of the 19th century, when punch cards were used to store patterns for silk weaving looms. Punch cards remained a viable form of data storage until the 1970s. Technology has evolved to include several types of mass storage devices:

Floppy Disk


Floppy disks are portable and can be removed from the drive itself. They are considerably slower and have less capacity than a hard disk, but they are very inexpensive. Floppy disks are small, either 5¼-inch or 3½-inch in diameter (the earliest floppy disks were 8 inches in diameter). 5¼-inch floppy disks were widely used until about 1987. 3½-inch floppy disks, encased in rigid plastic, are the most common type used today.

Hard Disk


Hard disks hold multiple gigabytes of data and have very fast access times. A hard disk consists of several platters, and each platter features two read/write heads (one for each side). Each platter has the same number of tracks, which are concentric circles placed on the surface of each platter. A cylinder is the collection of all tracks where the heads are currently located. This type of arrangement allows for random data access.

Optical Disk


Optical disks can hold several gigabytes of data, though not as much as hard disks. Optical disks use lasers to read and write data, instead of electromagnetism. While optical disks are inexpensive, access times are slower than a hard disk.

Tape


Magnetic tape consists of a long strip of magnetically coated plastic. The storage capacities of tape are quite large, up to several hundred gigabytes. Accessing data stored on tape, however, is considerably slower. Tape media is accessed sequentially, meaning that in order to get to any particular place on the tape, all the preceding data must be processed. Because of this, tape is best suited for long term data storage and system backups.

Mass storage should not be confused with memory, which refers to temporary storage areas within a computer system. Mass storage devices can retain data even when the computer is turned off, unlike the main memory of a computer. Storage is measured in kilobytes (1024 bytes), megabytes (1024 kilobytes), gigabytes (1024 megabytes), and terabytes (1024 gigabytes).