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Did You Know? … Some Salient Facts about Optical Discs.

Optical Disc Trivia

Did You Know?

We all hear about urban myths.  This isn’t one of them, but we at the ACE offices thought what about optical discs?  What ever possessed them to make the disc that size or the case that way?  Ever wonder about these things?

We at ACE always have and decided to do some research.

10 Facts about Optical Discs

After an exhaustive search, here are 10 interesting facts you may have never known about Optical discs.


  1. The Diameter of the Optical Disc is 120mm.  It is the diagonal width of a standard Compact Cassette from end to end.
  2. The thickness of a Optical Disc is 1.1mm +/- 0.2mm.  This includes the stacking ring which is molded into each and every discs.  It is this stacking ring that separates one disc from another.  By having this stacking ring one disc should not stick to another.  Because of this thin spacing between discs a vacuum is prevented from being created allowing automation to pick a single disc from a stack.
  3. A CD usually weighs around 0.53 of an ounce or 15 grams.  That’s a $0.70 stamp for first class USPS.  Who says freight isn’t expensive and that is just the disc, without packaging.
  4. Compact Disc technology is an evolution of Laser Disc technology, where a focused laser beam is used that enables the high information density required for high quality digital audio signals.
  5. Sony and Philips developed the technology independent of each other; eventually collaborating on a standard known as the Red Book.
  6. A CD is a single layer disc of polycarbonate on one side, a thin layer of aluminium, and a thin layer of lacquer beneath.  It is through this lacquer the laser beam reads the pits to generate music.
  7. A DVD can be several different formats (DVD-5, DVD-9 or DVD-10) but essentially they are all created the same way.  They are two layers of polycarbonate, glued together with a lacquer finish on the bottom.  Two lasers read the double layered disc.
  8. Laser Discs were made from acrylic; very hydroscopic (they tend to absorb water) and the plating will oxidize over time.  So folks with old laser discs please keep them in a dry, desiccant environment to prevent oxidation (delamination).  The use of polycarbonate for the current optical discs prevent oxidation.
  9. CD playing time was extended to 74 minutes to accommodate Wilhelm Furtwangler’s recording of Ludwig van Beethoven’s Symphony #9 from the 1951 Bayreuth Festival.  It was also meant to prevent Phillips who had a experimental factory at the time producing 115mm diameter discs from having a competitive advantage over Sony who did not have a factory at the time.
  10. Finally, CD’s hold almost 700 MB of data.  A Digital Versatile Disc can hold 4.7GB-9.4GB.  A Blu-Ray Disc (BRD) anywhere from 25GB to a staggering 128GB of data.

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