How to tell if media is a CD or a DVD

"You can't just through physical examination. Both are 120mm in diameter and 1.2mm thick.

If the manufacturer hasn't written something descriptive on the label (or on the text by the spindle hole) then you can't tell the difference just through observation.

If you have access to a high power microscope you could examine the surface of the disk as the pit sizes differ for CDs and DVDs, you'll find the pit are 0.74 µm for DVD versus 1.6 µm for CDs.

[Most DVD writing software (like CD burner XP or Nero) will tell you what type of disk is in the drive.]"

"As has been mentioned before in the comments, there is most definitely a way to determine if a disc is a CD or DVD through physical examination. It is actually quite obvious, DVDs are two sheets of polycarbonate sandwiching the recording layer, look at the edge of the disc, if you can see a thin trench down the middle, then it is a DVD.

They also sound different when you tap them against something, a DVD is a slightly lower, more dull thud. They also feel different to me, but that might just be me. :)"