Hardware Reference
In-Depth Information
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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 chan-
nel. 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
takesup4,500sectorsonthedisc(1minuteifmeasuredintime,orabout9.2MBworth
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).
•
Program (data) area
—This area of the disc starts at a radius of 25mm from the cen-
ter.
•
Lead-out
—The lead-out marks the end of the program (data) area or the end of the
recording session on a multisession disc. No actual data is written in the lead-out; it is
simply a marker. The first lead-out on a disc (or the only one if it is a single session
or Disk At Once recording) is 6,750 sectors long (1.5 minutes if measured in time, or
about 13.8MB worth of data). If the disc is a multisession disc, any subsequent lead-
outs are 2,250 sectors long (0.5 minutes in time, or about 4.6MB worth of data).
Figure 11.4
Areas on a CD (side view).
