Hardware Reference
In-Depth Information
crash or improperly read data needed for a calculation. Using the previous example with
a data CD running an executable program, guessing 15 is not merely slightly off—it is
completely wrong.
In a CD on which data is stored instead of audio information, additional information is
added to each sector to detect and correct errors as well as to identify the location of data
sectors more accurately. To accomplish this, 304 bytes are taken from the 2,352 that ori-
ginally were used for audio data and are instead used for sync (synchronizing bits), ID
(identification bits), ECC, and EDC information. This leaves 2,048 bytes for actual user
data in each sector. Just as when reading an audio CD, on a 1x (standard speed) CD, sec-
tors are read at a constant speed of 75 per second. This results in a standard CD transfer
rate of 153,600 bytes per second (2,048×75), which is expressed as either 153.6KBps or
150KiBps.
Note
Some of the copy-protection schemes used on audio CDs intentionally interfere with the au-
dio data and CIRC information in such a way as to make the disc appear to play correctly,
butcopiesoftheaudiofilesoroftheentirediscwillbefilledwithnoise.Copyprotection for
both audio and data CDs is discussed in more detail later in this chapter.
CD Capacity
Each second of a CD contains 75 blocks of data containing 2,048 bytes per block.
From this information, you can calculate the absolute maximum storage capacity of an
80-minute or 74-minute CD, as shown in
Table 11.3
. The table also shows the structure
and layout of each sector on a CD on which data is stored.
Table 11.3 CD Sector Information and Capacity
