Hardware Reference
In-Depth Information
The disc is divided into six main areas (discussed here and shown in
Figure 11.4
):
•
Hub clamping area
—The hub clamp area is just that: a part of the disc where the hub
mechanism in the drive can grip the disc. No data or information is stored in that area.
•
Power calibration area (PCA)
—This is found only on writable discs and is used only by
recordable drives to determine the laser power necessary to perform an optimum burn. A single
CD-R or CD-RW disc can be tested this way up to 99 times.
•
Program memory area (PMA)
—This is found only on writable discs and is the area where
the TOC (table of contents) is temporarily written until a recording session is closed. After the
session is closed, the TOC information is written to the lead-in area.
•
Lead-in
—The lead-in area contains the disc (or session) TOC in the Q subcode channel. The
TOC contains the start addresses and lengths of all tracks (songs or data), the total length of the
program (data) area, and information about the individual recorded sessions. A single lead-in
area exists on a disc recorded all at once (Disc At Once or DAO mode), or a lead-in area starts
each session on a multisession disc. The lead-in takes up 4,500 sectors on the disc (1 minute if
measured in time, or about 9.2MB worth of data). The lead-in also indicates whether the disc is
multisession and what the next writable address on the disc is (if the disc isn't closed).
