That's a bit of a bugger!
I did see this note:
Code:
Source: https://melog.info/archives/2004/09/30223144.html
It is nowadays ... The following extensions made with software BKDSK are all solid images.
The type of disk is distinguished by the extension.
The file size is used to calculate the number of tracks. (160 track use with 1024 × 8 sectors, etc.)
MS-DOS format
* .HDM → 2HD (360 rpm) 1024 bytes × 8 sectors × 154 tracks
* .HD5 → 2HD (360 rpm) 512 bytes × 15 sectors × 160 tracks
* .HD4 → 2HD (300 rpm) 512 bytes × 18 sectors × 160 tracks
* .DD6 → 2DD (300 rpm) 512 bytes × 8 sectors × 160 tracks
* .DD9 → 2DD (300 rpm) 512 bytes × 9 sectors × 160 tracks
N88-BASIC format
* .HDB → 2HD (360 rpm) 128/256 bytes × 26 sectors × 154 tracks
↑ track 0 only single density 128 bytes, others double density 256 bytes
* .DDB → 2DD (300 rpm) 256 bytes × 16 sectors × 160 tracks
https://github.com/barbeque/pc98-disk-t ... -japan.txtThis might imply that the .DD6 is always in MS-DOS format, if there is some way of identifying that, and that the DDB is always N88-Basic, which also might have a distinguishing mark, as it were. Otherwise, go with the extension. If you have some (probable) samples of each, I could try to take a look.