After Hours

Geek Trivia: A sound argument

Why did the original technical specification for the compact disc, agreed on by both Sony and Philips, set the diameter of the CD at 120 millimeters -- a somewhat controversial decision with some infamously unusual reasoning behind it?

When you say the words "red book," the average (non-engineer) person probably assumes you're referring either to Redbook magazine or the so-called Little Red Book, the nickname of the pocket version of Quotations From Chairman Mao Tse-Tung. However, audio technicians and audiophiles know the Red Book as shorthand for IEC 60908, the International Electrotechnical Commission's official specification for the compact disc.

The complete spec is proprietary and requires purchasing a license from Philips for a fee — between $200 and $5,000, depending on the format of the spec you're looking for. But most of the basics spelled out in the document are common knowledge and shaped the modern CD as we know it. They include:

  • A maximum playing time of 74 minutes, including pauses
  • A maximum of 99 tracks per CD
  • A disc diameter of 120 millimeters (mm)
  • A disc thickness of 1.2 mm
  • A center spindle hole diameter of 15 mm

This, of course, is just the tip of the techno-jargon iceberg, omitting such classics as non-return-to-zero, inverted binary; cross-interleaved Reed-Solomon encoding; and eight-to-fourteen modulation. Nonetheless, IEC 60908 has dictated the shape, size, operation, and function of nearly all compact discs since Philips released it in 1980 — two years before CDs ever hit the market.

Only recently have companies released CDs that don't comply with IEC 60908, and most of those violations are attributable to copy-protection schemes or dual-layer DVD/CD encoding. Suffice it to say, the vast majority of the 200 billion audio CDs sold since the compact disc's debut 25 years ago have conformed to the 60908 standard.

You'll note that we haven't mentioned Sony — the company most often associated with the creation of the compact disc. That's because Philips and Sony co-developed the CD, with much of the technology derived from Philips' existing (though ultimately unsuccessful) LaserDisc video efforts. When the first compact disc rolled off the assembly line on Aug. 17, 1982, that line was at a Philips plant in Germany.

The two companies collectively developed and agreed on the specifications found in IEC 60908, but the basis for at least one of those specs — the 120-mm diameter of the CD — was somewhat controversial, especially when you hear the possible reasoning behind it.

WHY IS THE COMPACT DISC STANDARDIZED AT 120 MM WIDE?

Get the answer.

About

Jay Garmon has a vast and terrifying knowledge of all things obscure, obtuse, and irrelevant. One day, he hopes to write science fiction, but for now he'll settle for something stranger — amusing and abusing IT pros. Read his full profile. You can a...

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