Factors:
| Channel bit code
| 8/14 + (3 merge bits) -> 8/16 EFM |
| Larger surface area utilization
| 86.0 to 87.6 square centimeters |
| Decrease in RS code
| 25% to 13% of channel rate |
| track pitch
| 1.6 to 0.74 microns |
| min pit length
| 0.972 to 0.4 microns |
| Reduction in packet overhead
| (2048/2352 to 2048/2060 bytes) |
Gain:
| Areal increase in channel bits
| 5.254
| ((1.6*0.972)/(0.74*0.40)) |
| Packet overhead reduction
| 1.142
| (2352/2060) |
| Tigher FEC
| 1.16
| (0.87/0.75) |
| Increase in usable area of disc
| 1.019
| (87.6/86) |
| Tighter channel code
| 1.0625
| (17/16) |
| Overall gain
| 7.5
| 4.7 / 0.65 GBytes
|
Note that the gain is less with
respect to pure Red Book audio packets since there is no CD-ROM
XA overhead in Red Book. The factor is then only about 6.6 : 1 gain.
This lower gain factor would be more typical of "DVD vs. CD" had
the original audio CD format (circa 1982) been designed with computer
data storage in mind. 2-D FEC product codes, frames instead of sectors
(small gain), and interleaving of sectors (large error correction
gain) could have been designed into the early CD standard, but would
have added more cost to players of the time.
Also, Red Book sets a rather large tolerance
for pit lengths (which affects scanning velocity) and track pitches.
The standard audio CD capacity of 74 minutes can be increased to
82 minutes using discs that push the edge of the spec.
