Hardware Reference
In-Depth Information
Figure 11.3. Typical components inside an optical drive.
When introduced, CD-ROM drives were too expensive for widespread adoption. After the
production costs of both drives and discs began to drop, however, CDs were rapidly assimilated into
the PC world. This was particularly due to the ever-expanding size of PC applications. Virtually all
software is now supplied on optical media, even if the disc doesn't contain data representing a tenth
of its potential capacity.
Tracks and Sectors
On the traditional 74-minute CD, the pits are stamped into a single spiral track with a spacing of 1.6
microns between turns, corresponding to a track density of 625 turns per millimeter, or 15,875 turns
per inch. This equates to a total of 22,188 turns for a typical 74-minute (650MiB) disc. Current 80-
minute CDs gain their extra capacity by decreasing the spacing between turns. See
Table 11.1
for
more information about the differences between 74-minute and 80-minute CDs.
Table 11.1. CD Technical Parameters
