From: tom.hornberger@verizon.net   
      
   Tom wrote:   
      
      
   > The WD1771 can generate a couple of Data Address Marks(think that's the   
   > correct term) that can't be generated by the WD1791.  Of course there's at   
   > least one of those Marks used by TRSDOS to mark one of the sector types.   
   > The MOD 3 & 4 have the WD1793 (I think), that's why a Mod 3 or 4 can't   
   > properly copy Mod I disks.   
   >   
   > HTH,   
   > Tom   
      
   Quick followup, the Mod I uses the FA Data Address Mark to mark the   
   directory sector under TRSDOS.  There's a good explanation at   
   http://www.tim-mann.org/trs80faq.html (item #12).  That's why you're stuck   
   with using the WD1771 to run the Single Density mode on the Mod I.   
      
   HTH,   
   Tom   
      
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