From: findlaybill@blueyonder.co.uk   
      
   On 18/12/2025 01:34, John Levine wrote:   
   > It appears that John Dallman  said:   
   >> ] * "Trap and Emulate� is an illusion of compatibility"   
   >> ]   * Performance differential is too great for most applications   
   >>   
   >> This is inevitably true nowadays, but wasn't when the idea was invented.   
   >   
   > For at least 20 years IBM's mainframes have used what they call millicode.   
   The   
   > relatively simple instructions are implemented in hardware, and everything   
   else   
   > in millicode, including the more complication instructions, I/O, and other   
   > system features. Millicode runs on the same CPU using the same instruction   
   set   
   > as regular code with some extra registers and instructions to handle aspects   
   of   
   > the hardware not visible to regular programs. It is stored in dedicated   
   memory   
   > which is loaded at boot time so it's easy to update.   
   >   
   > I gather there have been instructions that were implemented in millicode,   
   then   
   > moved into hardware in the next CPU generation since they were used enough   
   for   
   > the speed to matter.   
   >   
   > Here's a 2012 slide deck:   
   >   
   > https://public.dhe.ibm.com/eserver/zseries/zos/racf/pdf/ny_met   
   o_naspa_2012_10_what_and_why_of_system_z_millicode.pdf   
   >   
      
   Typical IBM boosterism of a minor variant of an existing technique,   
   as used (for range compatibility, etc) by the ICT 1900 Series in 1965   
   and before that (for h/w economy) by the Ferranti Atlas and Orion.   
   --   
   Bill F.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)