What's the improvement of DVD over CD ROM

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.

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