About the Floppy-geometry: in Virtual Box only multiples of 2/8 and 2/15 (ment ABOVE the standard floppies) seems to be rejected.
Today I tested all my FAT12 presets in the range from 160KB-1920KB: 160, 180, 320, 360, 400, 600, 640, 720, 800, 820, 1200, 1440, 1600, 1680, 1760, 1840 and 1920. In Virtual Box only 600k and 640k gave problems with Scandisk, all others were 'good'. In VMware 17 Player ALL where 'good'.
But now comes the interesting part: after my tests, I played a bit in VMware with the higher preset-floppies above 4MB. Highest one that worked was the 4320KB with 'SCANDISK.EXE /surface', already with size 5760KB the connection to the floppie even was 'removed' while checking surface ('removed' according to Scandisk):
BTW Afterwards 'DIR' still worked... Also: up to a size of 10800KB all Scandisk' tests except 'surface' were 'good', from 11520KB on the floppie was reported as 'removed' during normal testing already.
I took a look in the LOG:
2024-05-03T14:28:37.686Z No(00) vmx ConfigDB: Setting floppy1.fileName = "D:\FLOP36MB.IMG"
2024-05-03T14:28:37.729Z No(00) vmx ConfigDB: Setting ide1:0.fileName = "auto detect"
2024-05-03T14:28:37.729Z No(00) vmx ConfigDB: Setting floppy0.clientDevice = "FALSE"
2024-05-03T14:28:37.729Z No(00) vmx ConfigDB: Setting floppy1.clientDevice = "FALSE"
2024-05-03T14:28:37.803Z In(05) vmx FLOPPYLIB-IMAGE: Invalid number of cylinders (1024 while only 255 allowed)
2024-05-03T14:28:37.803Z In(05) vmx FLOPPYLIB-IMAGE: Could not detect floppy geometry from image file.
2024-05-03T14:28:37.803Z In(05) vmx FLOPPYLIB-IMAGE: Default 80/2/18 geometry used.
I did a quick search, only two sources mentioned the 255 cylinder 'barrier' (MS-DOS/floppie controller related):
https://www.syslinux...old/memdisk.php
https://wiki.osdev.o...Disk_Controller
My tool MKFATIMG.G4B takes CHS too, so I quickly made a FAT12 floppie with CHS 255/2/45, including MS-DOS boot code and system. I booted the floppie in VMWare, and this time Scandisk was fully 'happy' (including testing surface).
In case of El Torito floppies maximum CHS in VMWare with two heads would be respectively 255/2/15 (3825KB)), 255/2/18 (4590kBKB) and 255/2/36 (9180KB). Not as big as the floppies discussed in the thread you mentioned earlier: https://msfn.org/boa...oppy-emulation/, but still nice sizes. I will test these sizes with ISOHDR later.
The maximum with two heads will be 255/2/63. I made this floppy image as FAT12. After booting in VMWare, Scandisk found NO errors. Action print-screen of the floppie-specs and 'Scandisk surface':
BTW Sadly Virtual Box uses the 4MB-barrier in case of floppies, so no tests possible.
EDIT:
I remember I reported earlier El Torito-booting was just fine in VMware, which seems to conflict with the 255 cylinder floppie 'barrier'.
So I made a new 34560KB floppie image, pasted this in an old ready-made ISOHDR, and booted the iso in VMware 17 Player to the MS-DOS command-line.
Everything was still fine, Scandisk was 'happy' with all tests.
So the El Torito boot-floppies seems to be handled different in VMware, than 'normal' floppies described above.