From: muta...@gmail.com   
      
   On Friday, July 16, 2021 at 2:44:41 PM UTC+10, Joe Monk wrote:   
      
   > > There is an x'66' in front of the 16-bit op-code. It wouldn't   
   > > work otherwise.   
   > >   
   > > That's why we've been talking about x'66'.   
   > >   
   > Not Necessarily.   
   >   
   > "For programs executed in protected mode, the D-bit in   
   > executable-segment descriptors determines the default   
   > attribute for both address size and operand size. These   
   > default attributes apply to the execution of all instructions   
   > in the segment. A value of zero in the D-bit sets the default   
   > address size and operand size to 16 bits; a value of one, to 32 bits."   
   >   
   > So if the default is set correctly to 16-bits, then there wouldn't be an   
   instruction prefix.   
      
   Whether an instruction prefix is generated or not is dependent   
   on the assembler, not the descriptors used at runtime.   
      
   My assembler will generate the x'66'.   
      
   And there is no such thing as "correctly". PDOS/86 when   
   running on an 80386 in PM32 will set all the D-bits to 0   
   to keep everything 16-bit. That's the design. It isn't "incorrect".   
      
   BFN. Paul.   
      
   --- SoupGate-Win32 v1.05   
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