How DVD increased density over CD ROM

Channel bit code 8/14 + (3 merge bits) -> 8/16 EFM
Larger surface area utilization86.0 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 length0.972 to 0.4 microns
Reduction in packet overhead(2048/2352 to 2048/2060 bytes)

Areal increase in channel bits5.254((1.6*0.972)/(0.74*0.40))
Packet overhead reduction1.142(2352/2060)
Tigher FEC1.16(0.87/0.75)
Increase in usable area of disc1.019(87.6/86)
Tighter channel code1.0625(17/16)
Overall gain7.54.7 / 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.