I'm looking at disk image files for the Dragon 32 / Dragon 64 computers.
The Dragon computers are very similar to the Tandy TRS-80 Color Computer "CoCo" but are not clones and are not the same. In particular the two machines have very different Disk Operating Systems with totally different disk layouts. The Dragons run "DragonDos" while the CoCos run "RSDOS".
Both systems allow booting third-party OSes from the floppy boot sector by executing a command,
DOS on the CoCo and
BOOT on the Dragon.
Bootable floppy disk sectors begin with the signature
OS. On DragonDos, this is LSN (logical sector number) 2, or track 0 sector 3. (On a CoCo RSDOS disk the boot sector and
OS signature is on track 34 sector 0).
But I have some disk image files I downloaded (labelled "Dragon DOS 1.0 Boot" and "Dragon DOS 2.F Boot") which instead of an
OS signature at LSN 2 have a
DK signature in the same place. I cannot find this signature documented anywhere though the
DK signature is used for other things in the Dragon ecosystem:
DragonDOS was on a cartridge which puts the
DK signature at address
ROM OS: Appears in cartridge space $c000-dfff (Cumana system uses $c000-feff) Adds IRQ, FIRQ and NMI handling code, uses various Ram hooks ... $c000:c001 'DK' - used by BASIC Rom init to detect Disk Rom $c002-c003 Cartridge Init entry point (BRA $c0xx) $c004-c029 Indirect address table $c004:c005 Low Level Hardware Command byte routine ($cxxx) $c006:c007 ($00ea)
I never used these systems back in the day so they're unfamilar. I have three emulators but I find them more tricky to use than many emulators. Most emulate both CoCo and Dragon and I'm not sure how much guessing the emulator does when you try to load a file. Usually I can't get these images to work but sometimes I can't get any image to work. I'm never sure if I've got the right ROM images in the right folders, what needs Dragon 64 and not just Dragon 32. ROMs from one emulator don't always just work in another emulator that comes without ROMs. MAME is very counterintuitive in its microcomputer emulation setup...
So the question is, do both
DK indicate boot sectors? Is the
DK variant documented or not somewhere? Do I have disk versions of the cartridge? - the
00ea is in the same location as above but not everything matches. Do I maybe have something more recent from the retro era that's based on modified ROMs?