According to Sony, 120 million CD players and three billion CDs have been sold in the US alone.
The success of the CD - as if nobody knew it - is total. When was the last time you heard the word 'record'? Now a new revolution is upon us: the digital video disc or DVD. There is the DVD for video and the DVD-Rom for computer data.
The new medium looks almost exactly like the old; it is 120 millimetres in diameter and it is 1.2 mm thick. Looks, however, can be deceiving. The new DVD format holds seven times the data of the standard CD.
That translates into 4.7 gigabytes per layer - and there can be two layers with DVD. A disc with two layers can hold 8.5 gigabytes on one side.
The increase in data capacity is accomplished in a number of ways. First, the pit size is much smaller on DVD.
The pits are the holes or troughs that make up the bits of the data.
