The DVD
In 1995 the DVD (digital versatile disc) was developed, it is an optical medium and is very similar to CDs. As technology has advanced the size of the pits and the space between them can be decreased allowing more data for the same overall disc space. Also data error checking techniques have improved and so more actual data can be stored on DVDs compared to CDs. The final improvement is that slightly more of the usable area on the disc is used compared to CD. All this adds up to a disc with a capacity of 4.7gb but it does not stop there, DVDs can be dual layer and double sided giving a 12cm diameter 1.2mm thick polycarbonate disc a capacity of 17gb. The most common setup is single sided dual layer which gives a capacity of 8.5gb. DVDs are used mostly for film storage since they have the capacity to store high quality digital audio and video. They are also used for personal computer data backups, home video production and software distribution.