CD and DVD are optical stockpiling medium used to store advanced information. So apart from the capacity (a CD holds about 650 MB of data vs 4 to 9 GB for a DVD), there are of course other technical aspects which are as mentioned below :
- Bumps on the DVD are more dense and smaller as compared to CD-: The bumps etched on a DVD’s surface are roughly 4-times smaller than those on a CD. These bumps are known as pits and tracks. Each bits and tracks signifies 0 or 1 though which data is decoded . 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. This demonstrates the improvement in overall plastic molding technology within the decade that separates the CD’s advent (1982) to the DVD’s. A Blu-Ray’s surface is roughly 10 times more detailed than a CD. (as shown in fig 1.1).
2. Error and damaging
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. 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.
3. Laser and frequency requirements to calculate the disc data
DVD utilizes a more limited frequency laser with red light around 650 nm contrasted with a CD with infrared light at 780 nm.(table for which is shown below)
Extra knowledge 🔥🔥
- The data in these disc are calculated/written by IC known as optoelectronic IC. In these IC there is a laser attached which read and write data onto it. The frequency of these lasers are mentioned in above sections
- These discs can have various encodings like- : 2 channels of LPCM audio, each signed 16-bit values sampled at 44100 Hz
- this guy wants a analog disc -: In 1974, Lou Ottens, director of the audio division of Philips, started a small group to develop an analog optical audio disc with a diameter of 20 cm (7.9 in) and a sound quality superior to that of the vinyl record. However, due to the unsatisfactory performance of the analog format, two Philips research engineers recommended a digital format in March 1974. In 1977, Philips then established a laboratory with the mission of creating a digital audio disc. The diameter of Philips’s prototype compact disc was set at 11.5 cm (4.5 in), the diagonal of an audio cassette.
- Most of the design rights are still with sony and phillips
Experiment you can show your to your teacher and fellow classmates so that they believe you know about these disc and some other cool stuff like diffraction and interference
The trial is to gauge the track pitch and to decide the clear zone of the disc. The track pitch was dictated by directing laser light from a He/Ne laser onto the meaningful zone of a circle at ordinary occurrence to the disc. Measuring the space between the tracks by :
- To lead this test set up the plate as demonstrated in fig 3 when you switch on the laser light you ought to be seeing a brilliant spot on the paper straightforwardly under the circle alongside other diffraction in accordance with the laser.
- Then decide the situation of each spot on the paper and measure the distance (L) of laser pillar above paper.
- Now finally take the distance ‘w’ which is the distance between every diffraction spots.
- Take normal of atleast 5 readings.
- This research paper which is written by me lol -: GMSET-JD19-Ekansh-Agarwal.pdf (globusmedicaljournal.com)
- Hecht Optics, (2004). 4th Ed., 420.
- John A. Cop, (1993). The Physics of the Compact Disk. Physics Ed., 28, 15.
- Johannes Sturm, Martin Leifhelm, Harald Schatzmayr, Stefan Groiss Horst Zimmermann Infineon Technologies Austria AG Siemensstrasse 2, A-9500 Villach, Austria 1 Technical University of Vienna EMST Gusshausstrasse 25/354, A-1040 Wien, Austria firstname.lastname@example.orgOptical, Receiver IC for CD/DVD/Blue-Laser Application