PCjs v1.15.7 adds support for the XDF Diskette Format, which was used in PC-DOS 7.00.

However, this support is referred to as “fake” XDF support, because it requires using JSON disk images created by DiskDump without the experimental “–xdf” option, which is an option that attempts to encode XDF sectors as they existed on the original diskettes (ie, with varying lengths and non-standard sector IDs).

“Fake” XDF support works by using conventional 80-track disk images with 23 sectors/track. No standard PC floppy disk format ever used 23 sectors/track, but in this case, by distributing the XDF track data across 23 conventional 512-byte sectors, the PC-DOS 7.00 Setup code that reads XDF disks succeeds. This was probably one of several fall-back options built into the PC-DOS XDF code.

October 28, 2014