I am 50 and this is the first time I read about a 3” floppy.
Actually, it was 3.5” floppy, a tremendoun improvement over the 5 1/4” floppy.
The Zip Drive followed, but read/write CDs killed it.
I use my old 3.5” floppies for target practice.
The I recall the 3” disk format but there were other competing “mass” storage forms as well at the time including a mini-string tape transport, which used a small, short tape loop cartridge similar to 8 track (remember the trailing tapes going from the cartridge to the transport in your car when the tape got wrapped around the capstan?), a mini cassette system, all of which main claim was they were going to be less expensive to buy the external transport than the external floppy drive cost. All of them failed for the same reason, non-interchangeability with the main built-in 5 ¼” drive, not to mention poorly conceived designs and access speeds.