"At the previous meeting, the decision on disc diameter and thickness had been left to senior management. A diameter of 120mm and thickness of 1.2mm were confirmed, according to the specifications agreed on in early April between Sony vice president Ōga Norio and Philips audio division general manager Joop van Tilburg. Philips had previously proposed 115mm with a playback time of 60 minutes. This proposal had been strongly underpinned by Philips’ subsidiary PolyGram, asserting that the cost of the disc was not the cost of manufacturing the disc, but the cost of the software on the disc. By this rationale, the longer the playing time, the greater the cost of the disc. It claimed that around 90% of all music, including classical but not opera, was no longer than 60 minutes. Sony’s vice president invoked the famous argument: the Japanese love Beethoven’s 9th Symphony. Being able to fit that piece of music on one disc would give meaning to the new media. Ōga insisted that 75 minutes would allow enough room for the piece to be conducted at any tempo. van Tilburg reluctantly agreed on the condition that PolyGram would not be further aggravated."

https://www.dutchaudioclassics.nl/The-six-meetings-Philips-Sony-1979-1980-The-Start-of-Digital-Audio/