> The original floppy used on the mac was a single-sided 400KB disk. I imagine that was another set of trade-offs

Originally they planned on using custom 870K drives, but they were too unreliable so at the last minute they switched to the Sony 400K 3.5" disks

https://en.wikipedia.org/wiki/Apple_FileWare

https://folklore.org/Hide_Under_This_Desk.html