On Sat, 11 May 2019, Chuck Guzis via cctalk wrote:
In the case of RX50 on the PC, it doesn't matter. The format is 10 sectors of 512 bytes, which isn't supported by the PC BIOS in any regular sense (9 sectors is the norm). So most packages that deal with FILES-11 RX50 floppies on a PC use direct hardware (chip) access and bypass the BIOS completely. PUTR is one such package.
If the only problem is that there are 10 sectors per track, that can still be done WITH THE BIOS, using Int1Eh in conjunction with Int13h, except for the potential problems with 765 index "flash blindness". For formatting tracks, you can use Int1Eh to alter the sector gaps.
