Storage Basics

A data storage system has two main components: a storage medium and a storage device. A storage medium (storage media is the plural) is the disk, tape, CD, DVD, or other substances that contains data. A storage device is the mechanical apparatus that records and retrieves data from a storage medium. Storage devices include hard disk drives, tape drives, CD drives, and DVD drives. The term “storage technology” refers to a storage device and the media it uses.

You can think of your computer’s storage devices as having a direct pipeline to RAM. Data is copied from a storage device into RAM, where it waits to be processed. After data is processed, it is held temporarily in RAM, but it is usually copied to a storage medium for more permanent safekeeping. A computer works with data that has been coded into bits that can be represented by 1s and 0s. Obviously, the data is not literally written as “1” or “0”. Instead, the 1s and 0s must be transformed into changes in the surface of a storage medium. Exactly how this transformation happens depends on the storage technology. Three types of storage technologies are used for personal computer: magnetic, optical, and solid state.

Hard disk, floppy disk, and tape storage technologies can be classified as magnetic storage, which stores data by magnetizing microscopic particles on the disk or tape surface. Before data is stored, particles on the surface of the disk are scattered in random patterns. The disk drive’s read-write head magnetizes the particles, and orients them in a positive (north) or negative (south) direction to represent 0 and 1 bits. Data stored magnetically can be easily changed or deleted. This feature of magnetic storageprovides lots of flexibility for editing data and reusing areas of a storage medium containing unneeded data. Data stored on magnetic media such as floppy disks can be altered by magnetic fields, dust, mould, smoke particles, heat, and mechanical problems with a storage device. Magnetic media gradually lose their magnetic charge, resulting in lost data. Some experts estimate that the reliable life span of data stored on magnetic media is about three years. They recommend that you refresh your data every two years by recopying it.

CD and DVD storage technologies can be classified as optical storage, which stores data as microscopic light and dark spots on the disksurface. The dark spots are called pits. The lighter, non-pitted surface areas of the disk are called lands. Optical storage gets its name because data is read using a laser light. The transition between pitsand lands is interpreted as the 1s and 0s that represent data. An optical storage device uses a low-power laser light to read the data stored on an optical disk. The surfaceof an optical disk is coated with clear plastic, making the disk quite durable and data less susceptible to environmental damage than data recorded on magnetic media. An optical disk, such as a CD, is not susceptible to humidity, fingerprints, dust, magnets, or spilled soft drinks, and its useful life is estimated at more than 30 years.

A variety of compact storage cards can be classified as solid state storage, which stores data in a non-volatile, reusable, low-power chip. The chip’s circuitry is arranged as a grid, and each cell in the grid contains two transistors that act as gates. When the gates are open, current can flow and the cell has a value that represents a “1” bit. When the gates are closed, the cell has a value that represents a “0” bit. Very little power is required to open or close the gates, which makes solid state storage ideal for battery-operated devices. Once the data is stored, it is non-volatile – the chip retains the data without the need for an external power source.

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