Wasn't there a camera (Canon?) that used them? Or
was that a DIFFERENT
2.5"? - there were several competing 2.5" (and a 2.9" spiral)
technologies
being shown around that time.
Akai used a 2.8" spiral disk in a range of samplers in 1985. To add to
the confusion, the disks were called QD, for "quick disk". The whole
disk was read into memory in one read action, maybe that makes them quick.
http://www.vintagesynth.com/akai/s612.php
Fred Jan