Also, optical disks have been used for archival storage. Optical disks are now used in some models of personal computers, and they are expected to become more common. These are magneto-optic materials, phase-change materials, and thermoplastic materials. Among the candidate materials for erasable disks, three groups are more promising. Some of the materials used for nonerasable disks are tellurium, silver halide, photoresists, and photopolymers. This type of memory is needed for temporary data storage, such as in digital computing. In the second type, the recorded data can be erased or changed. The first type is useful for archival storage and storing data or instructions that do not need to be changed. Optical disks are of two types: read-only disks and read–write (erasable) disks. Optical disk is capable of storing 30 to 200 Mbytes of information. The main advantage of optical disks is their high storage capacity. A relatively new medium for data storage is optical disks, where the information is recorded and read by a laser beam. Today, magnetic hard disks and floppy disks are widely used in electronic computers. Mir Mojtaba Mirsalehi, in Encyclopedia of Physical Science and Technology (Third Edition), 2003 VI.C.3.a Optical disks The disk motor spins all the time that a disk is present. There are generally no switches or status indicators, the simple action of moving a flap on the front of the drive to load or removing the diskette being the only operator action. Transfer rates are below 300 kilobytes per second.Īnother simplification is in the area of operator controls. Access times, imposed by the rather slow head-positioning mechanism using a stepping motor, are in the range of 100-500 ms. Eventually, however, wear and therefore error rate are such that the diskette may have to be replaced, copying the information onto a new diskette.Ĭapacities vary from the 256 kilobytes of the earliest drives, which record on one surface of the diskette only, to a figure of over 2 megabytes on more recent units, most of which use both surfaces of the diskette. This feature and the choice of disk coating and the pressure loading of the head are such that, at the rotational speed of 360 rev/min, the wear on the recording surface is minimal. This runs in contact with the disk surface during read/write operations and is retracted otherwise. One major simplification in the design of the floppy disk system is the arrangement of the read/write head. The compactness and flexibility of the disk makes it very simple to handle and store, and possible for it to be sent by post. Diskettes are of three standard diameters, approximately 203 mm (8-inch), 133 mm (5 1/2-inch) and 89 mm (3 1/2-inch). As the name implies, the magnetic medium used is a flexible, magnetic oxide-coated diskette, which is contained in a square envelope with apertures for the drive spindle to engage a hole in the centre of the disk and for the read/write head to make contact with the disk. The floppy disk, while having the four elements described above, was conceived as a simple, low-cost device providing a moderate amount of random access back-up storage to microcomputers, word processors and small business and technical minicomputers. Ian Robertson, in Mechanical Engineer's Reference Book (Twelfth Edition), 1994 4.12.6 Floppy disk
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |