CD ROM READER SERIES

It should be noted that if the surface of CD-ROM becomes dirty and scratched, it will reduce its readability. Lasers are illuminated on the reflective surface of the disk to read patterns of pits and platforms lands ('pits', the gaps between them referred to as 'lands').Д«ecause the depth of the pits is about one-quarter to one-sixth of the laser wavelength used to read the CD, the phase of the reflected beam shifts relative to the incident beam, which causes destructive interference and reduces the intensity of the reflected beam.

CD ROM READER SERIES

Read Principle of CD-ROMДata is stored on the disc as a series of micro-indentations. The most common CD-ROM size is 120 mm in diameter, but smaller MINI CD is 80 mm in diameter, as well as various non-standard sizes and molded compact discs. The disc is made of 1.2 mm thick polycarbonate plastic disc with a thin aluminum layer and can be made into a reflective surface. Meanwhile, they store and retrieve data in a very similar way (unlike audio CD in the standard for storing data only). Appearance of CD-ROMД¬D-ROM is the same in appearance as audio CD. Some CD-ROMs store both music and computer data, then the music can be played by a CD player, while computer data can be processed by a computer. In 1985, the Yellow Book standard developed by SONY and Philips made this format adaptable to a variety of binary data. This kind of CD format was originally designed for the storage and playback of music. Information stored on the disc will be read by the disc drive during use. This type of disc can only write data once, then the data on the disc is read-only which cannot be altered or erased, and the information will be permanently stored on the disc. A CD-ROM is a type of computer memory in the form of a compact disc which contains data. LetвЂ™s get to know it!Д¬D-ROM Stands for Compact Disc Read-Only Memory. The contents of the article are all about CD-ROM, in this part, you will get to know what is CD-ROM based on three aspects. What Is CD-ROM: Definition, Appearance and Read Principle

Features of CD-ROM: Capacity, Usages, Advantages and Disadvantages.

What Is CD-ROM: Definition, Appearance and Read Principle.

Therefore, additional error correction codes are used when storing data on a CD-ROM. When data is stored on a CD, however, any data error is catastrophic.

If a few bytes are misread in music, the worst thing that can happen is a little fuzz during playback.

The drive actually reads data one revolution at a time, and un-interleaves the data in order to play it. This problem is solved by actually interleaving the data on the disc, so that it is stored non-sequentially around one of the disc's circuits.

Because a scratch or a speck on the CD might cause a whole packet of bytes to be misread (known as a burst error), the drive needs to be able to recover from such an event.

To solve this problem, extra data bits are added that allow the drive to detect single-bit errors and correct them.

Because the laser may misread a bump, there need to be error-correcting codes to handle single-bit errors.

Subcode data can encode the absolute and relative position of the laser in the track, and can also encode such things as song titles.

This problem is solved using what is known as subcode data. Because the laser wants to be able to move between songs, data needs to be encoded into the music telling the drive 'where it is' on the disc.In EFM, 8-bit bytes are converted to 14 bits, and it is guaranteed by EFM that some of those bits will be 1s. To solve this problem, data is encoded using EFM (eight-fourteen modulation). Because the laser is tracking the spiral of data using the bumps, there cannot be extended gaps where there are no bumps in the data track.