This question already has an answer here:
It's an open question whether desktops would've kept using 5.25" until the end of the floppy era, but laptops meant something smaller was going to be introduced; that much was essentially predetermined. The contingent historical fact was the adoption of the particular 3.5" format we all remember, in preference to the many others that were contenders at the time.
I was reading this Wikipedia page just now and came across this:
"In the early 1980s, a number of manufacturers introduced smaller floppy drives and media in various formats. A consortium of 21 companies eventually settled on a 3 1⁄2-inch floppy disk (actually 90 mm wide) a.k.a. Micro diskette, Micro disk, or Micro floppy, similar to a Sony design but improved to support both single-sided and double-sided media, with formatted capacities generally of 360 KB and 720 KB respectively."
So the way Wikipedia puts it, sounds like the decision was basically made by committee. Twenty-one companies got together, carried out a sober evaluation of all the contenders based on technical merit, manufacturing cost, which influential members already had a large investment in what, etc, then issued a verdict and so it was done.
My understanding had been a bit different. As I understood it from e.g. here the big breakthrough for the 90 mm format that ended up winning, was getting into the Macintosh, for which Apple helped Sony debug the drives (their own Twiggy drives developed for the Lisa, never having become reliable enough). I assumed this was the reason they started being used in PC compatible laptops, which settled the matter.
If that version of the history is correct, the outcome was determined not so much by a grand deliberate decision from all interested parties, as by a few particular events, decisions made by a handful of individuals who were trying to solve their own short-term problems; a historical accident, chaos at work in the technical sense of the word.
Which version is accurate?