CD-ROM.

CD-ROM.

Land Disk Pit coil Focusing Objective Lens Prism Light-sensing diode Laser diode Sectors

1 - The motor constantly changes the rotational speed of a CD-ROM disk, no matter where the component named
detector relative to the disc radius. The portion immediately below the detector always moves at the same speed. (See note below.)

2 - The laser projects concentrated beams of light that pass followed by a coil focusing (focusing coil).

Note - Discs such as those used in magnetic hard disk drives have the data arranged in concentric circles
called tracks, which are divided into sectors in the radial direction. Through a scheme known as angular velocity
constant when the magnetic disk rotates at the same rate, i.e., the tracks near the outer edge of the disc move more
faster than the tracks near the center.
As the external sectors pass under the heads faster read / write, they must be physically larger to
can store the same amount of data that the domestic sectors. This format wastes a lot of space
on the disk, but maximizes the speed with which data is read.

Note - Commonly, CD-ROM uses a different scheme of magnetic disks to mark the areas of the disk that
the data are recorded. Instead of several tracks arranged in concentric circles, the CD-ROM data are,
in a single spiral track moves towards the center of the disc. The trail is also divided into sectors, each sector but
occupies the same physical size. Through the method known as constant linear velocity, the disk varies
continuously rotating the disc. Thus, when the switch moves to the center of the disc, it slows down. The
effect allows the CD contains more than one magnetic disk sectors and therefore, a larger amount of data. When the
detector moves toward the center of the disk, the velocity decreases, allowing time for the data to be read from disk.
A new type of CD called MultiSpin, far outweighs the CD.

3 - The laser beam penetrates the protective layer of transparent plastic material and has a reflective layer resembling an aluminum foil at the bottom of the disk.

4 - The surface of the reflective layer ALTEMA among the highest areas, or protrusions (pits), and the tiny low-lying areas or recesses (lands). These records form the two surfaces 1 and 0 used to store data.

5 - Upon finding a projection (pit) light is scattered but achieving a groove (land) returns directly to the detector by passing through a prism (prism) which deflects the laser beam to the photosensitive diode (light-sensing diode).

6 - Each pulse of light that hits the photosensitive diode generates a small potential difference (DDP) electric. DDPS These combine with a timer circuit to generate a stream of ls and Os that the computer can understand.

Source: Evolution of Computers