DVD/CD track spacing and storage capacity

[NeoXx]

Hello,

I finished an experiment of finding out the track spacing of a CD and a DVD.
My laser wavelength was 654nm which I used to calculate track spacing of the optical discs.

I got a track spacing of a CD 1.57um which is close to a real value of 1.6um,
and the track spacing of a DVD 0.72um which is close to a real value of 0.74um.

Then I calculated the storage capacity of both and got 654 Megabytes for a CD which is pretty good but only 2786 MB for a DVD, which is pretty far from its true value of 4700 MB.

What did I do wrong?

Oh here's the worksheet I used to calculate the storage capacity:
http://www.teachengineering.org/collection/uoh_/activities/uoh_diffraction/uoh_diffraction_activity1_worksheet_mhf_tedl.pdf

Regards,

NeoXx

 

[DrClaude]

Then I calculated the storage capacity of both and got 654 Megabytes for a CD which is pretty good but only 2786 MB for a DVD, which is pretty far from its true value of 4700 MB.

Please show your work.

 

[NeoXx]

This is my second experiment where I got similar data as one mentioned in my first post.

 

[dauto]

Not all DVD's store 4.7 G bytes. Some DVD-RAM store 2.5 G bytes. May be that's what you used?

 

[NeoXx]

Not all DVD's store 4.7 G bytes. Some DVD-RAM store 2.5 G bytes. May be that's what you used?

But as far as I know all DVD types have the same track spacing?

As well, I measured the track spacing similar to a normal DVD, and still got 2.8GB...