
I-28 Computer Fundamentals
A CD is a shiny, silver colour metal disk of 12 cm in diameter. A typical optical disk is made
up of three layers: a polycarbonate base through which light can pass, a layer of aluminium
and a protective layer of acrylic on top of that. The pits of CD are typically 0.5 microns wide,
0.83–3 microns long and 0.15 microns deep. A CD has one track that spirals from the centre to
the outside edge. If one could remove the track from a standard 12 cm CD, it would stretch for
three and a half miles. The single track is divided into sectors of equal length and density. Files
are stored on these particular contiguous sectors. ...