Sharp DV-500D Technical Manual page 5

1-6 Order and Direction of Disc Recording
There are 3 types of recording orders and directions.
1 layer disc
Center of the disc
2 layers disc (A)
Center of the disc
2 layers disc (B)
Center of the disc
1-7 Two Discs are Stacked Together to Form DVD discs
The DVD disc structure is the stacking of two 0.6mm thin type discs, making it most suitable for
reading high density recorded data signals.
The thinner the disc, the less number of obstacles between pits notched on the optical pick up and
disc, so more precise reading can be achieved.
Additionally, stacking these same material discs together back-to-back, increases evenness,
meaning the disc will warp less due to heat and humidity compared to single 1.2mm boards. Thus,
the discs are more reliable.
0.6mm
0.6mm
DVD (stacked-together structure)
Features of the 0.6mm Thick Disc
1. Materialized mass capacity and high density
• Because the thickness is half that of traditional discs, it is less likely to warp or slant.
• Degree of evenness becomes much higher at assembly, with high rates of evenness and
precision.
2. Makes board-making easier and reduces production costs
• The stacked structure is highly resistant to environmental changes (heat, humidity)
• The thin structure increases the time cycle, so forming is easier stabilized
• Overall, it will cost less than 20% more than a CD.
Lead-in area
Parallel track path
2
Lead-in area
1
Opposite track path
Lead-out area
Lead-in area
1
Changes in temperature and humidity
5
Data area
Data area
2
Data area
CD (single board structure)
DVD-Series
Lead-out area
Lead-out area
Middle area
1.2mm