CD-ROM

Cd drives work my using optical media. Data is stored by burning microscopic indentations into the disc. A pattern of indentations is then created in a spiral pattern in order to store data. The absence of an indentation is used to help create the pattern. Effectively these pits and lands can be used to store binary data.

DVD-Rom uses the same techniques as a CD-Rom however data is stored on two layers. Two lasers of differing wave length are used to read the different layers. Also the pits and lands are stored closer together meaning that the laser must be more accurate.

These types of media tend to be used to store multimedia information or programs. For example DVD movies and music CD’s. Programs such as Microsoft office are distributed on this type of media. Due to their light weight and large capacity sizes this means a lot of high quality multimedia can be stored on them. They are also cheap to mass produce.

RAM (random access memory) CD’s can store multimedia or user data onto CD’s. This is ideal for backing up small to medium sized files. When a CD is created you will not be able to modify it. As such it is good for creating a permanent backup ranging over a period of time. As they are small it will not take up too much storage space. Re-writable CD’s exist which allow the user to write to them many times. These can be used in situations where you only need one backup and that backup needs updating regularly.