From: joemonk64@gmail.com   
      
   > In a canonical sense, a CCW isn't code (from the perspective   
   > of the host CPU), although as I understand it, some lower-end   
   > 360 systems didn't offload the CCW to the channel controller,   
   > but rather processed it (perhaps in microcode) in the CPU...   
      
   Not just 360s. There were also 370 machines (i.e. 43XX) that had integrated   
   channels.   
      
   Point is, at the hardware level, there is no way to distinguish code from   
   data. A perfect example is the EX instruction. You can dynamically use "DATA"   
   to modify code, and then execute the modified code.   
      
   Example: I need to change a CLI (compare) to check for a ZERO instead of an   
   'A'...   
      
   I@EX     EQU   *   
   * Execute   
            LA    R3,X'F0'        Use X'F0' as second byte of CLI   
            EX    R3,I4EX       * EXECUTE CLI INST at CLI ADDRESS   
   ...   
      
   I4EX     CLI   ALPHA1,C'A'   
   ...   
      
   ALPHA1   DC    CL26'ABCDEFGHIJKLMNOPQRSTUVWXYZ'   
      
      
   Joe   
      
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