It implements different techniques for the error correction i.e., RS-PC and recording code EFMPlus. 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 renders videos with excellent picture quality and random access. 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. There are several variations of the compact disc such as CD-R, CD-ROM, CD-RW. Indented portion of the disk reflects back the light which is detected by the photodetector. The stored bits are read through targetting the laser light on to the polycarbonate part of the spinning disk. , and the length and width of the pit are 0.8-3 and 0.5 microns respectively. 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. In the last part, the disk is stamped by a label. The thin aluminium material covers the programmed disk, and a protective acrylic then coats this aluminium layer. The flat or unindented area is known as the land. This layer also provides a clear glass base. The CDs first layer is constructed by the polycarbonate plastic which stores the data in the indented pits. It was a suitable replacement for the magnetic disk as it offered the low-cost solution for storing a significant amount of 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. The CD (Compact Disc) was the first step towards the idea of digital encoding of the data.
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