计算机外文翻译-----大容量存储器(编辑修改稿)

计算机外文翻译-----大容量存储器(编辑修改稿)内容摘要：

cturer , resulting in what are known as formatted disks. Most puter systems can also perform this task. Thus, if the format information on a disk is damaged, the disk can be reformatted, although this process destroys all the information that was previously recorded on the disk. The capacity of a disk storage system depend on the number of number of disks used and the density in which the tracks and sectors are placed. Lowercapacity systems consist of a single plastic disk known as a diskette or, in those cases in which the disk is flexible, by the less prestigious title of floppy disk. (today’ s 3 1／ 2inch diameter floppy disks are housed in rigid plastic cases, which do not constitute as flexible a package as their older 5 1／ 4inch diameter cousins that were housed in paper sleeves.) Diskettes are easily inserted and removed from their corresponding read/write units and are easily stored. As a consequence, diskettes are often used for offline storage of information. The generic 3 1／ 2inch diskette is capable of holding of data but nongeneric diskettes are available with much higher capacities. An example is the Zip disk system from Iomega Corporation, which provides storage capacities up to several hundred MB on a single rigid diskette. Highcapacity disk systems, capable of holding many gigabytes, consist of perhaps five to ten rigid disks mounted on a mon spindle. The fact that the disks used in these systems are rigid leads them to be known as harddisk systems, in contrast to their floppy counterparts. To allow for faster rotation speeds, the read/write heads in these systems do not touch the disk but instead “float”just off the surface. The spacing is so close that even a single particle of dust could bee jammed between the head and disk surface, destroying both (a phenomenon known as a head crash), Thus harddisk systems are housed in cases that are sealed at the factory. Several measurements are used to evaluate a disk system’s performance:(1)seek tome (the time required to move the read/write heads from one rack to another)。 (2)rotation delay or latency time (half the time required for the disk to make a plete rotation, which is the average amount of time required for the desired data to rotate around to the read/write head once the head has been positioned over the desired track)。 (3)access time (the sum of seek time and rotation delay)。 and (4)transfer rate (the rate at which data can be transferred to or from the disk). Harddisk systems generally have significantly better characteristics than floppy systems. Since the read/write heads do not touch the disk surface in a hareddisk system, one finds rotation speeds of several thousand revolutions per minute, whereas disks in floppydisk systems rotate on the order of 300 revolutions per minute. Consequently, transfer rates for harddisk systems, usually measured in megabytes per second, are much greater than those associated with floppydisk systems, which tend to be measured in kilobytes per second. Since disk systems require physical motion for their operation, both hard and floppy systems suffer when pared to speeds within electronic circuitry. Delay times within an electronic circuit are measured in units of nanoseconds (billionths of a second) or less, whereas seek times, latency times, and access times, and access times of disk systems are measured in milliseconds (thousandths of a second). Thus the time required to retrieve information from a disk system can seem like an eternity to an electronic circuit awaiting a result. Compact Disks Another popular data storage technology is the pact disk (CD). There disks are 12 centimeters ( approx。