This could have some general usefulness, so I'll post a way to calculate approximate location on a DVD.
- A standard sized DVD is 120 mm in diameter, or a radius of 60 mm.
- The data is stored between a radius of 24 mm and a radius of 58 mm, starting at the inner circle and working out.
- The data is stored at a uniform density.
So a full standard disk is storing 4.7 GB on 8,759 mm2 of media surface, or 1,864 mm2 of surface per GB.
Say you're interested in where the 2.5 GB boundary is. That will require the inner 4,659 mm2 of media surface (2.5 x 1,864), which surrounds a 24 mm radius "hole" (1,810 mm2). So the boundary will be a circle with an area of 4,659 + 1,810 mm2, or 6,469 mm2. That circle has a radius of 45.4 mm.
Measuring a cheap DVD of mine, the actual diameter was 119 mm rather than 120, or a radius of 59.5 mm. So give or take the actual dimensions and rounding error, the 2.5 GB boundary would be 14 to 15 mm from the outer edge.