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Technology 101

It seeks the improvement of user’s knowledge by supplying information about technical part of ODD product.

Disc Structure 1

1. Compact Disc

Track Pitch : 1.6um
– 1mm = 625 tracks
– 1 CD = 20,000 tracks,or 5km
– Number of Pits = 6 billion
Lead In Area : Φ46mm ~ Φ50mm
The Lead-in contains the TOC data, including number of tracks, length of each track and the total length of the whole tracks.

Program Area : Φ50mm ~ Φ116mm
Lead Out Area : 0.5mm wide (Φ117mm) area that comes next to the Program area from the inside.
The data are stored in a single spiral track of pits.

2. Pit

Pit Width : 0.4 ~ 0.5um (related to the laser wavelength)
Pit Length : 3T ~ 11T (1T = length covered per clock cycle)
CD Clock : 4.3218MHz =>7.35KHz x 588
ex) CD Constant Linear Velocity(CLV) = 1.25m/s
T = 1.25(m/s) / 4.3218(MHz) = 0.2892um
3T = 0.8677um, 11T = 3.1815um
CLV : In Constant Linear Velocity (CLV) systems, the relative speed between the data spiral and the playback or record head is constant. To achieve this, the rotational speed of the disc needs to vary according to the radial position of the pickup. The rate varies from 1.2 m/s ~ 1.4 m/s.
CAV : In Constant Angular Velocity (CAV) systems, the disc rotates at the same speed. Therefore, the relative speed between the data spiral and the playback head increases as the pickup moves outward.
Jitter : The time fluctuation of the pit position.
3T jitter is the central measurement since it’s when the data get most unstable and sensitive.
Transfer rate : The speed at which a certain volume of data is transferred from a device to a host such as a personal computer. It is usually measured in bits per second or bytes per second.
CD 1X = 150KB/sec , DVD 1X = 1350KB/sec
3. CD Diagram
CDs are digitally played back using light and not touching the disc physically.
Basically, CDs have one playback side.
CDs are written onto using a laser.
Protective layer is quite strong and doesn’t get scratches easily.
ven if there are some scratches, you don’t have to worry as long as they don’t affect the reflective metal layer; since a laser beam doesn’t go through the protective layer.
Scratches or dusts on the play side won’t be any trouble so long as they don’t block the 1 mm-wide laser beam completely.