From: joe@user.com   
      
   "Tom Lake"  wrote in message   
   news:46d717d5$0$18903$4c368faf@roadrunner.com...   
   >   
   > "N Morrison"  wrote in message   
   > news:1188497343.934188.156010@i38g2000prf.googlegroups.com...   
   > >   
   > > There are no ROMs - just a small boot ROM to load and execute the boot   
   > > sector on the floppy. It's really basically a Z-80 emulator that is   
   > > needed.   
   >   
   > You'd need to emulate the ROM to some extent to boot a TRSDOS   
   > disk image.  At least the part that SEEKs to the proper directory and   
   > loads the boot files.  Also the error message or Diskette? message   
   > issued when there is no boot file (or did the Model II just hang like the   
   > Model I?)   
   >   
      
   The Model II was different and pretty advanced for it's day.   
      
   First off, the Model II was 'loadable' in the sense that there was NO   
   operating ROM in the machine.  There was a small boot ROM that   
   loaded a 'mini' loader in single density from the 8" floppy.  Then the   
   system kicked into more of a 'real' mode in that it used DMA to   
   read the rest of the diskette double density.  Everything was then   
   loaded into RAM.  (The Model II was TOTALLY RAM in operation,   
   no ROM space at all.)  There were a few different versions of the   
   boot ROM, but they all worked pretty much the same way.  Only   
   adding boot capability like the HD.   
      
   Since there wasn't a standard ROM in the Model II, that means you'd   
   need a lot more than a Z80 emulator, you'd need to also emulate   
   all the chips in the Model II, since you wouldn't know how the chips   
   were used and then use that to 'load' whatever version of TRSDOS   
   you wanted to operate.   
      
   On the other hand, it might be a lot easier to write an emulator that   
   was DOS restricted and at that point would work with the 'DOS'   
   functionality already 'built in'.  That would mean unfortunately that   
   some software wouldn't work if it went to the hardware in weird   
   ways, but software that worked that way was rare except for the   
   backup protected stuff like P&T CP/M.  There were diskettes that   
   were run protected, like the Model II diag disks that kept trying to   
   force a backup from the original disk, but those used the DOS   
   sector int calls in TRSDOS 2.0 versions. (Which unfortunately were   
   gone from the TRSDOS 4.x versions.  A really poor decision in my   
   opinion, but that's just my opinion, a giant step backwards.)   
      
   Mike   
      
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