Information stored in a mass storage system is conceptually grouped into large units called files. A typical file may consist of a complete text document, a photograph, a program, a music recording, or a collection of data about employees in a company. We have seen that mass storage devices dictate that these files be stored and retrieved in smaller, multiply byte units. For example, a file stored on magnetic disk must be manipulated by sectors, each of which is a fixed predetermined size. A block of data conforming to the specific characteristics of a storage device is called a physical
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A common property of mass storage systems based on magnetic or optic technology is that physical motion, such as spinning disks, moving read/write heads, and aiming laser beams, is required to store and retrieve data. This means that data storage and retrieval is slow compared to the speed of electronic circuitry. Flash Memory technology has the potential of alleviating this drawback. In a flash memory systems, bits are stored by sending electronic signals directly to the storage medium where they cause electrons to be trapped in tiny chambers of silicon dioxide, thus altering the characteristics of small electronic circuits. Since
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Another class of mass storage systems applies optical technology. An example is the compact disk (CD). These disks are 12 centimeters in diameter and consists of reflective material covered with a clear protective coating. Information is recorded on them by creating variations in their reflective surfaces. This information can then be retrieved by means of a laser beam that monitors irregularities on the reflective surface of the CD as it spins.
CD technology was originally applied to audio recordings using a recording format known as CD-DA (compact disk-digital audio), and the CDs used today for computer data storage use essentially
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