The CD-ROM should be considered mandatory on any computer that is built today, because most software is distributed on CD-ROMs. Nowadays, although still used, are beginning to fall into disuse since they began to be replaced by DVD drives. This is mainly due to the greater possibilities of information and a DVD-ROM capacity exceeds one CD-ROM. But who are the CD and DVD? A CD-ROM (English acronym Compact Disc – Read Only Memory, “Compact Disc – Read Only Memory”) is a compact disc used to store nonvolatile data. The CD is a flat plastic disc with digital information encoded in a spiral from the center to the outer edge. A standard CD can hold 650 or 700 MB data. To broaden your perception, visit Discovery Communications. The CD is popular for distributing software, especially multimedia applications, large databases and weighing only 30 grams. A DVD on the other hand are divided into two categories: single layer and double layer. A related site: David Zaslav mentions similar findings. The Virgin of single layer DVD can store 4.7 gigabytes, about twelve times more than a standard CD. The DVD uses a more efficient coding method in the physical layer: systems for detecting and correcting errors used in the CD, such as cyclic redundancy check CRC. But computer users will want to keep your own information and that is where born the CD and DVD Virgin Virgin. And made by the recorders or burners for either CD or DVD. A CD drive is an electronic device that allows the reading of these discs by using a beam of a laser beam and the subsequent transformation of these into electrical impulses that the computer interprets. These discs are written by CD recorders on the CD-R (blank CD) with the difference that makes the reader otherwise, ie, transform electrical pulses in a laser beam on the CD stored as binary data wells and plains. The same applies to the DVD burner but in this case are DVD-R. We can also find another category of cd and dvd rewritable. A Unlike CD-R, CD-RW discs themselves can be erased, or formatted (using your record, losing some of its capacity, but allowing new record in the file). In the case of using a CD-RW when we delete, erase it completely, it can also make partial deletion, which require more laser power to re-recorded. A CD-RW can be used as a floppy, with appropriate software, provided that the unit supports this feature, you can manipulate files as a floppy disk, with the exception that is not deleted, but deleting a file that is occupying a space on the disk, but does not appear to examine the file. CD-RW discs need more laser power to be recorded, therefore rewritable discs have a recording speed lower than write-once discs (take longer to finish recording). Cleaning and storage and the disk to store all data in full and for a very long time, it is necessary to keep the disc in the packaging or places incorrect. The reflective part of the disc should be clean and free of scratches, to prevent data loss. It is advisable to transfer data from an old disk or eroded, another disc clean or new, before they lose all the data over time. Only recommended to clean the disk if it is very dirty and breaks are image and / or sound recording or read errors. Since the error correction systems can read data through a moderate amount of scratches and / or fingerprints.