I've updated our sys with support for DR/PC/MS DOS in addition to FreeDOS on FAT12/FAT16 only. For PC/MS DOS support you must define WITHOEMCOMPATBS when you compile sys. To support DR-DOS or any OEM DOS that uses IBMBIO.COM/IBMDOS.COM, loads at 0x70:0, and merely needs the full IBMBIO.COM loaded simply use the /OEM switch. Additionally, if /BOOTONLY not specified and KERNEL.SYS not found, it will automatically try IBMBIO.COM (and if found switch to mode same as if /OEM given). This should allow a stock FreeDOS sys to be used with the DR-DOS enhancement project and probably other 7.0x DR DOS versions. If compiled in, an alternate boot sector that is compatible with several versions of PC/MS DOS is used by specifying /OEM:PC or /OEM:MS (the MS option causes the use of IO.SYS instead of IBMBIO.COM in the compatible boot sector). This alternate boot sector only loads up to 29KB of the boot file [0x70:0-0x7C0:0], leaves 0x0:7C00 unchanged, and sets a few registers prior to the jump. [This is my best guess, it works on a floppy for me, tested with several flavors, however I used several techniques including a dummy IBMBIO.COM and my DOS references to figure out this info, so may not always work.]
Note: when using sys with PC/MS DOS, I advise formating the disk first and making no label to ensure the files are the 1st entries and occupy 1st data sectors; otherwise the IBMBIO.COM component may fail to finish the boot process. PC DOS 7R1 does not seem to require them at the beginning, but IBMDOS.COM does still seem to need to directly follow IBMBIO.COM. Later versions of MS DOS (such as WinMe, Win9x not yet tested) do not work with it.
Anyway, I did this for my own use, as I tend to want to create bootable DOS diskettes from existing ones, but find it a annoying to have to boot a particular DOS or find its sys.
Jeremy
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