From: rick.c.hodgin@gmail.com   
      
   On Friday, April 5, 2019 at 2:41:46 PM UTC-4, James Harris wrote:   
   > Does anyone here know what would likely happen to cache lines and buses   
   > if one were to read addresses which had no RAM - with or without caching   
   > enabled for those addresses? Ditto writing such addresses? Would the   
   > reads/writes cause problems? What value would be read? All zeroes? All   
   > ones?   
   >   
   > And would such operations be slower than accessing real RAM? I guess not   
   > but I don't know. Accessing non-existent RAM is not something one gets   
   > to do too often!   
      
   In developing my OS, I used this mechanism to determine how much   
   memory the machine it's booting on had.  I would write a non-zero   
   value to every 1 MB above the first 1 MB and when I read back a   
   zero, I know it was beyond the top of memory.  I could then iter-   
   ate backwards to find the maximum byte that has write access with   
   persistence.   
      
   --   
   Rick C. Hodgin   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)