storage devices

1. Optical Disk
 Is a flat, usually circular disc which encodes binary
data (bits) in the form of pits (binary value of 0 or
off, due to lack of reflection when read) and lands
(binary value of 1 or on, due to a reflection when
read) on a special material (often aluminum] ) on
one of its flat surfaces.

2. Compact Disk
- is a digital optical disc
data storage format. The
format was originally
developed to store and
play sound recordings only
(CD-DA), but was later
adapted for storage of data
(CD-ROM).

3. CD ROM
(compact disk read-only-memory)

4.  The disk format is identical to that of audio
compact disks, so the same dust-free
manufacturing plants that are now
stamping out digital versions of Mozart or
Mary Chapin Carpenter can easily convert to
producing anything from software to an
encyclopedia. Furthermore, CD-ROM
storage is large -up to 660 megabytes per
disk, the equivalent of over 400 3-1/2 inch
diskettes.

5. DVD ROM
Digital Versatile Disk
Read-Only-Memory
- DVD-ROM drives can
read data, such as stored
commercial videos for
playing. DVD-RW allow
DVDs to be created on a
computer

6. DVD
Digital Versatile Disk
is a flat disk, the size of a CD - 4.7 inches diameter and .05
inches thick. Data are stored in a small indentation in a
spiral track, just like in the CD. DVD disks are read by a
laser
beam of shorter wave-length than used by the CD ROM
drives. This allows for smaller indentations and increased
storage capacity. The data layer is only half as thick as in
the
CD-ROM. This opens the possibility to write data in two
layers. The outer gold layer is semi transparent, to allow
reading of the underlying silver layer. The laser beam is set
to two different intensities, strongest for reading the
underlying silver layer.