Why a DVD stores almost 30 times more information than a CD?

Options

A. DVD uses shorter wavelength lasers of 6350A but CD uses an infarred laser of 7800A
B. CD uses shorter wavelength laser compared to a DVD
C. CD works on the principle of diffraction
D. DVD Works on diffraction of light

Answer

To understand why a DVD stores almost 30 times more information than a CD, we can analyze the differences in their physical characteristics and the technology used in each.

### Step-by-Step Solution:

1. **Understanding the Basics**:
- A CD (Compact Disc) and a DVD (Digital Versatile Disc) are both optical storage media used to store digital data.
- The primary difference in their storage capacity lies in the technology and the physical structure of the discs.

2. **Laser Wavelength**:
- CDs use a laser with a longer wavelength (approximately 780 nm, which is in the infrared range).
- DVDs use a laser with a shorter wavelength (approximately 650 nm, which is in the red light spectrum).
- The shorter wavelength of the laser used in DVDs allows for a finer focus on the data pits.

3. **Pit Size and Density**:
- The data on CDs is stored in the form of pits and lands (the flat areas between pits).
- DVDs have smaller pits compared to CDs, which means more pits can be packed into the same physical area.
- This increased density allows DVDs to store significantly more data than CDs.

4. **Layering**:
- DVDs can have multiple layers (dual-layer DVDs can store even more data).
- CDs typically have a single layer, which limits their storage capacity.

5. **Data Encoding**:
- DVDs use more advanced data encoding techniques, which further increase the amount of data that can be stored compared to CDs.

### Conclusion:
Due to the use of a shorter wavelength laser, smaller pit sizes, the ability to have multiple layers, and advanced data encoding techniques, DVDs can store approximately 30 times more information than CDs.