Backward Compatibility of Optical Media

By · Tuesday, March 15th, 2011

Backward Compatibility of Optical CD, DVD & Blu-ray MediaIf you are not a wizard when it comes to CD and DVD technology, this article is for you! Optical media such as CD, DVD, and Blu-ray discs look very similar to one another. They are the same size, shape, and very close in weight. However, optical media discs are not universally interchangeable. Today I’m going to talk about why this situation exists and which formats are backwards compatible.

The first 120mm optical disc was the Compact Disc (or CD), which made its commercial debut in 1982. CDs had to be played in a compact disc player, such as a set-top unit in a home stereo or in a portable CD player. These devices were not compatible with any pre-existing media formats such as compact cassettes or 8-track tapes.

When the Compact Disc first came out, many people resisted buying it because it was not compatible with their existing library of music. This is a problem that engineers sought to avoid in the future by making devices that are backwards compatible. This means that when a new technology comes out like DVD discs, the player will also be able to work with existing formats such as CDs.

However, there have been a proliferation of optical media formats since 1982. Today we live in a world of CD, Blu-ray, and DVD discs. HD-DVD was with us only for a short while, and the future contains formats such as Blu-ray 3D and Blu-ray XL. Some players will play all of these formats, while others are restricted to only playing certain types of discs.

The big question is: which discs will work in which types of players? If all of this sounds confusing, it’s really not. To help illustrate which discs work in which machines, I have made this handy table:

Backward Compatibility of Optical MediaAs you can see, an audio CD is just about the easiest disc in the world to play back. If you have a machine that has a disc drive, chances are it will play a CD,  DVD discs were invented after the CD, and they are able to be played back on a DVD player and everything newer.

HD-DVD is a tricky format. Most all HD-DVD players support traditional CD and DVD discs in addition to their native HD-DVD format. However, newer discs such as Blu-ray and Blu-ray 3D will not work in an HD-DVD player, regular DVD player, or CD player.

Blu-ray discs are the latest and greatest trend in home entertainment and data storage. These discs will only work on hardware with the Blu-ray Disc Association logo, however the players are capable of viewing DVD and CD discs as well. Blu-ray disc players cannot watch HD-DVD movies, and vice versa.

Some Blu-ray players can receive a firmware upgrade to support Blu-ray 3D movies, though I should mention that a compatible TV is required in order to view the images in 3D.

So why don’t all types of discs work in all types of players? The discs look the same and fit into the same machines, but sometimes they do not play, such as when you insert a Blu-ray movie into a DVD player.

The reason has to do with how each of the different discs are manufactured and played. CDs, DVDs, and Blu-ray discs are recorded and played back by a laser beam that reads the information on the disc. CDs use a red laser which has a wavelength of 780 nanometers. DVD discs use a 450-nanometer laser, while Blu-ray discs use a 405-nanometer laser.

In the years since CDs were first introduced, the cost of producing red lasers has come down dramatically. This makes it easier for manufacturers to incorporate them into newer devices like DVD players and Blu-ray players. Older devices like CD and DVD players cannot read Blu-ray media because their lasers are not fixed to the proper wavelength of light to read the information on the discs.

I hope this article has been helpful in explaining the idea of backwards compatibility as it relates to optical media. Hopefully you will have a better understanding of which discs work in which players and why.

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