Ever looked at a CD and a DVD, or a DVD and a Blu-Ray (BD) disc and wondered what the difference was between them? After all, they both look exactly the same. Read on to find out the secret difference!

How They Basically Work – Audio CDs and CD-ROMs

At a basic level, CD, DVD and Blu-Ray discs all operate using similar principles. They store digital data encoded as a series of “pits” and “lands” (tiny indented and flat areas respectively) in a very fine spiral. This is read by a laser which follows the spiral.

Compact Disc Digital Audio (music CDs to you and me) came first, of course. This uses an infrared laser to read the spiral of data from the inside of the disc to the outside edge (the opposite direction to vinyl records).

With music CDs, the digital data capacity is used to hold audio (i.e. music). But since digital data in its simplest form is all basically the same, it was quite easy to adapt the format to hold computer data instead (as with CD-ROMs) with no major changes to the underlying technology.

How DVDs and Blu-Ray Improve On This

DVD works in a very similar way- at a basic level the discs are simply digital data holders. That data can carry video (as with DVD Video discs), audio or other computer files. However, the underlying technology has been improved- with DVDs, the pits and lands are smaller and the spirals are closer together. This means that much more data can be fitted onto a disc.

This means that the laser has had to be slightly upgraded to read the finer detail. Instead of the infra-red laser that CDs use, DVDs need a red laser that has improved reading resolution.

Blu-Ray Discs (BD or BD-R) have even smaller pits and lands and the spiral is even more tightly packed. The laser has had to be upgraded again, this time it’s violet-blue… hence the name Blu-Ray!

(Note that this is a pretty simplified explanation. CD-R, DVD-R and BD-R use dyes whose reflectivity can be changed by a write-laser instead of the “pressed” pits of prerecorded discs, but the other than that are much the same as their counterparts. The way that the extra data capacity of DVD and Blu-Ray is used to store higher definition video and the like is another issue altogether, and one we won’t bore you with!)

Conclusion

So the basic technology underpinning CD, DVD and Blu-Ray is pretty similar, but significantly refined with each generation. That’s why DVD can store far more than CD, and Blu-Ray can store far more than DVD.

It’s like comparing the old 78 RPM records with the later 33 and 45 RPM ones. The newer records work in essentially the same way, but refined the underlying technology so that the grooves were finer, a smaller needle was required and more music could be fitted in at higher quality.