CD-ROM

         The CD-ROM is stand for Compact Disk Read Only Memory is a technology taken directly form the audio world that has become standard equipment for computers. This is an optical and read only storage device.

CD-ROM

CD-ROM Construction

        Then term CD ROM refer to both the discs themselves and the drive that reads them. A CD is made of a polycarbonate wafer, 120mm in diameter and 1.2mm think with a 15mm hole in the center.  This wafer base is stamped or molded with a single physical track in a spitch or spiral configuration starting from the inside of the disc and spiraling outward. The track has pitch or spiral separation, of 1.6 microns (millionths of a meter, or thousandths of a millimeter).

CD-ROM Construction

CD-Writeable

      There are two main type of recordable CD drives and discs are available. One of them is called CD-R (recordable) and the other is CD-RW (rewriteable). All the CD-RW drives can also function as CD-R drives. All drives sold today are CD-RW. Those drives can work with either CD-R or CD-RW discs.

      Once a CD-R is written with data, it  is permanently stored and can’t be erased. The wite-once limitation makes this type of disc less than ideal for system backups or other purpose in which it would be preferable to reuse the same media over and over however, because of the low cost of CD-R discs is as economically feasible as tape or other media. In a CD-R the writing process is completed be burning an organic dye.

CD-RW discs can be reused up to 1000 times making them suitable for almost any type of data storage task. Most recordable CD drives are both CD-R and CD-RW in one. In a CD-RW the writing process is completed by phase change of a metal alloy. The writing speed of a CD-RW is less then a CD-R.

The capacity of a CD-R or CD-RW in normally 650MB to 700MB.

CD-Writeable