muta...@gmail.com  wrote:   
   > The other thing I would like to reconcile is MVS's slip   
   > trap for storage alter.   
   >   
   > I think the same thing could be done with the 80386   
   > by trapping every instruction and checking the storage   
   > to see if it has been altered.   
   >   
   > I wonder if the S/3X0 had some special hardware   
   > feature to detect alteration of storage.   
      
   That looks like trap on page fault.  All modern processors   
   can do this.  On 486 (and some other processors) there is   
   also another possibility: you can use debug registers   
   to trap access to specific address.  Debug registers   
   have advantages:   
   - you can trap on specific address   
   - there is choice, you can trap when storage changes, but   
     also on reads or in case of execution (normal breakpoints   
     do not work on ROM).   
      
   Disadvantage is that some processors have no debug registers   
   and usually number of debug registers is quite small.   
      
   --   
                                 Waldek Hebisch   
      
   --- SoupGate-Win32 v1.05   
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