SEB070016-TUTORIAL5

TYPE OF DIRECT ACCESS STORAGE DEVICE












Magnetic Disk


DESCTIPTION
A memory device, such as a floppy disk or a hard disk, that is covered with a magnetic coating. Digital information is stored on magnetic disks in the form of microscopically small, magnetized needles, each of which encodes a single bit of information by being polarized in one direction (representing 1) or the other (representing 0).
Magnetic disc is the primary computer storage device. Like tape, it is magnetically recorded and can be re-recorded over and over. Disks are rotating platters with a mechanical arm that moves a read/write head between the outer and inner edges of the platter's surface. It can take as long as one second to find a location on a floppy disk to as little as a couple of milliseconds on a fast hard disk


EXAMPLE
HARD DISK AND FLOPPY DISK


ADVANTAGES
high storage capacity,
reliable gives,
direct access to data.

Optical Disk


DESCRIPTION
Is an electronic data storage medium from which data is read and written to by using a low-powered laser beam. It is flat, circular, plastic or glass disk on which data is stored in the form of light and dark pits. The laser beam reads the pits and the data can be accessed


EXAMPLE
Read-only optical disk,WORM,Rewritable/Magneto-optic disks


ADVANTAGES
An optical disk has much more storage capacity on the order of gigabytes, than a magnetic disk. It can hold up to 6GB of data in comparison to 1.44 MB of a diskette. Optical disks are inexpensive to manufacture. Data stored on optical disks is resistant to power surges or magnetic disturbances, such as head crashes or corruption form stray magnetic fields. Hence, they provide high data stability. Optical disks are less vulnerable to extremes of hot and cold as compared to the magnetic disks. Optical disks have long media life than magnetic disks.















Flash Memory

DESCRIPTION
Flash memory is non-volatile computer memory hat can be electrically erased and reprogrammed. It is a technology that is primarily used in memory cards and USB flash drives for general storage and transfer of data between computers and other digital products. It is a specific type of EEPROM (Electrically Erasable Programmable Read-Only Memory) that is erased and programmed in large blocks; in early flash the entire chip had to be erased at once. Flash memory costs far less than byte-programmable EEPROM and therefore has become the dominant technology wherever a significant amount of non-volatile, solid-state storage is needed.


EXAMPLE
thumb drive, key drive, and mini-USB drive.


ADVANTAGES
The advantages of flash memory as compared with HDDs are substantial. They include smaller size, lighter weight, a far lower power consumption, longer life expectancy and greatly improved shock resistance.
















Magneto-optical Disk

DESCRIPTION
A magneto-optical drive is a kind of optical disc drive capable of writing and rewriting data upon a magneto-optical disc


EXAMPLE
magneto optical drive


ADVANTAGES
A magneto-optical disc comprising a recording layer and a protective coating on a substrate is operated for magneto-optical recording in a magnetic field modulation mode such that the protective coating is in sliding contact with a magnetic head.