though of course it's tricky building a 720k
6.22.system disk.
Not particularly. Stick a 3.5 inch double-density (not high-density) disk
into a standard PC 3.5 inch drive, and say "format b: /s /f:720".
Unlike 5.25 inch drives, where there are interchange problems with 360K
disks written in 1.2M drives, high-density 3.5 inch drives can write 720K
format with no problems. This is because both the 720K and 1.44M formats use
the same track pitch and track width.