Why are CDs 12cm?
It could be the stuff of legend, but it’s a good one. From Marginal Revolution:
Sony had initially preferred a smaller diameter, but soon after the beginning of the collaboration started to argue vehemently for a diameter of 120mm. Sony’s argument was simple and compelling: to maximize the consumer appear of a switch to the new technology, any major piece of music needed to fit on a single CD…Beethoven’s Ninth Symphony was quickly identified as the point of reference — according to some accounts, it was the favorite piece of Sony vice-president Norio Ohga’s wife. And thorough research identified the 1951 recording by the orchestra of the Bayreuther Festspiele under Wilhelm Furtwängler, at seventy-four minutes, as the slowest performance of the Ninth Symphony on record. And so, according to the official history, Sony and Philips top executives agreed in their May 1980 meeting that “a diameter of 12 centimeters was required for this playing time.”
Update: Soon after posting this, I was sent this link by @eesn which debunks the above story. I’m yet to read this full page, but so far it’s even more interesting than the original anecdote:
Everyday practice is less romantic than the pen of a public relations guru, as at that time, Philips’ subsidiary Polygram –one of the world’s largest distributors of music– had set up a CD disc plant in Hanover, Germany. This could produce large quantities CDs with of course, a diameter of 115mm. Sony did not have such a facility yet. If Sony had agreed on the 115mm disc, Philips would have had a significant competitive edge in the music market. Sony was aware of that, did not like it, and something had to be done.
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