3.1+IO+CD+and+DVDs

__**CD-ROM (compact disc read-only memory), DVD (digital versatile/video disk) readers and burners **__ __Input/Output? __ The CD itself is actually a__"Portable storage device"__ as it can store the information that it is given, they store information that we feel we might need at a later date or as a back-up tool. The DVD Reader is an __Input__ device as it places the disc onto the system; it's the DVD Burner that is actually the __Output device__, as it places the information onto the disc, thus taking the information out onto the disc.

__How does it work? __ A laser burns small grooves into the surface of the CD. The grooves have pulses in them which can later be read by a laser and detector. The pulses represent data, ones and zeros. Computers only know ones and zeros, so that works out just fine. The groves are organized into concentric circles. Some of the groves have special purposes and are there to identify the location and size of data stored on the CD-Rom. When your computer wants to read a file of a specific name, it searches the file TABLE, for the location and size of the named file, then the "read head" moves to that location and reads pulses that represent the data. ([]) To transfer data onto a blank DVD media in a way that is readable by the DVD player, the burner must record a digital pattern of reflective and non-reflective areas. To do this, a moving write laser has to alter the surface of the disc. Just like the read laser of a DVD player, the write laser follows the same spiral path. Pre-pressed grooves guide the laser along the outwardly path starting at the center of the disc. Even if it seems complicated, it is quite simple how the burner writes data to a blank disc. As the disc spins, a mechanism calibrates the rate of the spin with the speed of the laser. The laser must run along the path at a consistent rate of speed in order to give the precision needed for this sort of job. To create the 1s and 0s, the burner turns the laser on and off. It is turned on to darken the dye to represent the 0s, or bumps. It is then turned back off to encode the 1s, or flat areas, and leaves the dye translucent. ([]) DVD reader is a drive which opens by either a button or by the control panel. Once open you place a DVD – R/DVD-RW/DVD+R/DVD+RW/CD-R/CD-RW, and the reader will scan it with a laser, check if it is readable. If it is then it will simply play it. A DVD is the same size, physically, as a standard CD-ROM but can hold between 4.7 and 17 GB of information, depending on how the information is stored. A single – layer DVD can hold up to 4.7 GB of information. A second layer approximately doubles the data capacity of the disc.

__Where is it used? __ They are all simply used in households to access information, or play games or DVDs. On most computers there is access to a CD-ROM so the majority of people are able to access it at home or on the move (train etc.) by using a laptop.