From: david.brown@hesbynett.no   
      
   On 18/12/2025 19:20, Rosario19 wrote:   
   > 8 bit cpu for access memory other than 0..255 location has need at   
   > last one 16 bit register and 16 bits operations, so i think that even   
   > a 8 bit cpu has to have int in C language as 16 bits   
      
   No, 8-bit cpus don't need 16-bit registers or 16-bit operations.  8-bit   
   cpus typically only have 8-bit general registers (though most will have   
   a 16-bit PC register).  Some will allow you to use a couple of 8-bit   
   registers in a pair, primarily for memory addressing, but a pair of   
   8-bit registers is not the same as a 16-bit register.   
      
   And of course some 8-bit cpus don't have direct access to more than 256   
   memory locations - support for anything more is indirect in some way   
   (using page registers or other arrangements).   
      
   It is fair to say, however, that most "big" 8-bit cpus have either one   
   or more 16-bit address registers, or a reasonable way to combine two   
   8-bit registers in a pair for use in addressing.  And many such "big"   
   8-bit cpus have a few 16-bit operations, such as for loading or storing   
   a register pair, or incrementing or decrementing them.   
      
   And all this is simply saying that if a processor is going to be able to   
   access more than 256 bytes of memory with reasonable efficiency, it has   
   to be able to handle pointer sizes of 16-bit without too much overhead.   
   It says nothing about the need for a general data size greater than   
   8-bit (and "int" is for general data, not pointers or addresses).   
      
   For 8-bit devices, using 16-bit data for logic, arithmetic, counters,   
   data movement, etc., is significantly slower than using 8-bit.  That's   
   why they are called 8-bit devices.   
      
   C plays by different rules - it is defined on an abstract machine, not   
   any particular hardware.  It says that the size of an "int" is   
   implementation-defined, but it must be at least 16 bits.  Thus any C   
   implementation for 8-bit processors will have 16-bit ints - not because   
   it is a good size for the device (it certainly is not), but because   
   otherwise it would not be C.  (The size of pointers is not specified by   
   the standard - though you can infer a minimum of at least 15-bit data   
   pointers for hosted systems, 12-bit data pointers for freestanding   
   systems, and 12-bit function pointers.)   
      
   The C requirement for a minimum size of 16-bit int, together with the   
   integer promotion rules, is one of the reasons C was often considered   
   inefficient and inappropriate for small 8-bit microcontrollers.  In the   
   heyday of 8-bit microcontrollers, many were programmed in assembly   
   rather than C.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)