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Storage Devices Optical Drives
Optical drives refer to any disk drive that uses optical media, such as CDs, DVDs, or Blu-ray disks. Each disk has a different storage capacity due to the different wavelength of light the laser uses to read the disk, with shorter wavelengths enabling more data to be stored in the same physical space. CDs use infrared light, which has a long wavelength. DVDs use a red laser light, a light with a medium wavelength. Blu-ray uses a blue laser light, which has the shortest wavelength. A CD can hold 700 MB of data, or 80 minutes of music, a DVD can hold 4.7 GB on a standard disc and 8.4 GB on a dual-layer disc. Blu-ray disks can hold 25 GB on a standard disk and 50 GB on a dual-layer disc. Most contemporary workstations have a DVD writer, but Blu-ray writers are becoming more common. Also, each successive technology is backward compatible with the others, therefore a Blu-ray player can also read DVDs and CDs. However, a CD or DVD player cannot read a Blu-ray.
The different devices use different nomenclature for their capabilities. A CD-ROM, DVD-ROM, and BD-ROM (Blu-ray) all indicate that the device is a read-only memory (ROM) device. A device that is recordable only once is identified with an “R.” On a CD-R, DVD-R, DVD+R or BD-R, the contents of the disc cannot be changed after writing it the first time. The third category of devices are identified as “RW” devices, and known as write-many, write/rewrite, or erasable. This category includes CD-RW, DVD-RW, DVD+RW, DVD-RAM, and the BD-RE disc types.
The speed of an optical drive is described using an “X-rating.” The original CD players could read at 1X (one times), or 150 KBps. The 1X speed is the speed at which your audio CD drive plays your favorite song. DVD players operate at 1.385 MBps (so that is the 1X speed for that type of device). Blu-ray players operate at 4.5 MBps. When buying a drive, you will see the rating listed, such as a 52X CD player, which means it operates 52 times as fast as the original 150 KBps, or 7800 KBps, which is 7.8 MBps. The 1X for each device is the equivalent to listening to a music CD, watching a DVD, or watching a Blu-ray movie in a traditional player.