From: joemonk64@gmail.com   
      
   > > 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".   
      
   x'66' is operand size override prefix.   
      
   It flips the operand size from 16 to 32 when the D-bit is 0, and from 32 to 16   
   when the D-bit is 1. Of course, It only works for the 1 instruction it   
   prefixes.   
      
   So is that what you want? All operands to be 32 bit when the D-bit is 0?   
      
   Table 17-1. Effective Size Attributes https://www.scs.stanford.e   
   u/05au-cs240c/lab/i386/s17_01.htm   
      
   Segment Default D = ...         0     0     0    0    1     1    1    1   
   <-------   
   Operand-Size Prefix 66H       N    N    Y    Y    N    N    Y    Y <-------   
   Address-Size Prefix 67H       N    Y    N    Y    N    Y    N    Y   
      
   Effective Operand Size      16   16   32   32   32   32   16   16 <-------   
   Effective Address Size      16   32   16   32   32   16   32   16   
      
   Y = Yes, this instruction prefix is present   
   N = No, this instruction prefix is not present   
      
   Joe   
      
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