CD stands for Compact Disc was the primary step towards the thought of digital coding of the info. It uses a novel methodology of coding within which a 14-bit code indicates a computer memory unit and this coding technique conjointly helps in error detection. it had been an acceptable replacement for the memory device because it offered the low-priced answer for storing a big quantity of knowledge. DVD stands for Digital Versatile Disk provides another for the videotape utilized in tape recorder (Video container Recorder) and fixed storage utilized in computer because the videodisc will acquire seven times larger quantity of the info relative to CD. It renders videos with wonderful image quality and random access. A videodisc is constructed from a similar material because the CD however the method and therefore the layers area unit completely different, it’s used from each of the edges like 2 CDs area unit projected along. In DVD, RS-PC and EFMplus are used as the error correction codes.

1. ProfessorAjals CLASSES – 890 730 5642
ProfessorAjals CLASSES – 890 730 5642
Definition of CD
The CD (Compact Disc) was the first step towards the idea of digital encoding of
the data. It uses a unique method of encoding in which a 14-bit code indicates a
byte and this encoding technique also helps in error detection. It was a suitable
replacement for the magnetic disk as it offered the low-cost solution for storing a
significant amount of data.
The CDs first layer is constructed by the polycarbonate plastic which stores the
data in the indented pits. This layer also provides a clear glass base. The flat or
unindented area is known as the land. The thin aluminium material covers the
programmed disk, and a protective acrylic then coats this aluminium layer. In the
last part, the disk is stamped by a label. The pits are organised into the spiral
track, in the outward direction from the middle of the disk, though decreasing the
risk of damage by storing the index information at the start of the disk. , and the
length and width of the pit are 0.8-3 and 0.5 microns respectively.
The stored bits are read through targetting the laser light on to the
polycarbonate part of the spinning disk. Indented portion of the disk

2. ProfessorAjals CLASSES – 890 730 5642
ProfessorAjals CLASSES – 890 730 5642
reflects back the light which is detected by the photodetector. There
are several variations of the compact disc such as CD-R, CD-ROM,
CD-RW.
Definition of DVD
The advent of DVD (Digital Versatile Disk) provided an
alternative for the videotape used in VCR (Video Cassette Recorder)
and CD-ROM used in PC as the DVD can acquire 7 times larger
amount of the data relative to CD. It renders videos with excellent
picture quality and random access. A DVD is built from the same
material as the CD but the process and the layers are different, it is
used from both of the sides such as two CDs are sticking together.
It implements different techniques for the error correction i.e., RS-
PC and recording code EFMPlus. The reasons why it provides greater
size than a CD are – dense packing of the bits, use of shorter
wavelength laser and generation of the two-sided disc (data can be
read from write to both the sides). To obtain the smaller spacing
about 0.74 microns between the spiral tracks and the minimum
distance of 0.4 microns between the pits a short wavelength laser is
used.

3. ProfessorAjals CLASSES – 890 730 5642
ProfessorAjals CLASSES – 890 730 5642
It also employs a dual layer of pits and lands on the standard layer
and a semi-reflective layer on the top of the reflective layer. To read
the content of the layers separately in a DVD the laser must be
carefully focused. Similar to CD, DVD also has variants such as
DVD-R, DVD-RW, etcetera.
Difference between CD and DVD
CD stands for Compact Disc was the primary step towards the thought of digital coding of the info.
It uses a novel methodology of coding within which a 14-bit code indicates a computer memory unit
and this coding technique conjointly helps in error detection. it had been an acceptable replacement
for the memory device because it offered the low-priced answer for storing a big quantity of
knowledge.
DVD stands for Digital Versatile Disk provides another for the videotape utilized in tape recorder
(Video container Recorder) and fixed storage utilized in computer because the videodisc will acquire
seven times larger quantity of the info relative to CD. It renders videos with wonderful image quality
and random access. A videodisc is constructed from a similar material because the CD however the
method and therefore the layers area unit completely different, it’s used from each of the edges like
2 CDs area unit projected along. In DVD, RS-PC and EFMplus are used as the error correction
codes.
There are few differences between CD and DVD, which are given below:

4. ProfessorAjals CLASSES – 890 730 5642
ProfessorAjals CLASSES – 890 730 5642

5. ProfessorAjals CLASSES – 890 730 5642
ProfessorAjals CLASSES – 890 730 5642

6. ProfessorAjals CLASSES – 890 730 5642
ProfessorAjals CLASSES – 890 730 5642
Key Differences Between CD and DVD
1. A compact disk can hold up to 700 MB of data while a digital
versatile disk can hold a maximum 17 GB of data.
2. As the DVD can acquire a larger size, it is more prevalently
used than a CD.
3. The metal layer used for recording is placed beneath the
labelling side in the CD. In contrast, in DVD this metal layer is
situated in the centre of the disk.
4. The layers of pits and land on a CD can be only one whereas in
DVD it can be two.
5. A CD contains the spacing of 1.6 micrometres between spiral
tracks and 0.834 micrometres between the pits on the disc. On
the other hand, the spiral loops in DVD are 0.74 micrometres
apart and the distance between the pits is 0.4 micrometres.
6. The error correcting codes used in CD are CIRC and EFMP. As
against, DVD uses distinct error correction techniques which
involves RS-PC and EFMPlus.

7. ProfessorAjals CLASSES – 890 730 5642
ProfessorAjals CLASSES – 890 730 5642
7. The removal of the adhesive label of a CD can cause the
severe damage to the CD. On the contrary, when the adhesive
label of the DVD is removed, the imbalance in spin is caused.
Conclusion
The CD and DVD are the optical recording medium where CD was
devised as an audio storage format while DVD is used as the
universal storage format. The latter technology DVD can hold data
about 7 times more than CD and its format efficiency is also 32%
greater than a CD