XPost: alt.lang.asm, alt.os.development   
   From: james.harris.1@nospicedham.gmail.com   
      
   On 06/01/2018 15:34, Frank Tetzel wrote:   
      
   ...   
      
   > Why not add a 1:1 mapping of micro-ops to the ISA?   
      
   Perhaps the main reasons are to do with compatibility. For example,   
   Intel CPUs of today have to run many of the binaries of years ago. They   
   therefore need the same encodings. New encodings could be provided in   
   addition to the current ones but they would require lengthy   
   instructions. And they themselves would define new encodings that would   
   be expected to be preserved to future CPUs.   
      
   In fact, any micro-op encoding now would tend to lock itself in whereas   
   designers of later CPUs might want to change the internal encoding - and   
   we would be back to square one. So a translation from machine code to   
   internal encoding is not unreasonable.   
      
   Of course, the use of micro-coded instructions is not usually thought of   
   as a good idea now, with RISC approaches being faster.   
      
      
   --   
   James Harris   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)