Integer limits - unsigned.
  Real world vs. Computers.

  Available memory
 
  Standard work unit (byte).

  CPUs work because they can do simple standardized tasks, repeatedly,
    and very quickly.

    Variability at hardware level, such as variable sized numbers, 
      introduces cost and complexity.  

    Most CPUs work with fixed sized data.

    Although some exceptions exist.

      IBM 360 Decimal Pack instructions. 
        Operands specify start location of target data and number of digits.
   
    CPUs with fixed data sizes use flags to provide variability economically. 
 
      Zero - result zero or not.
      Carry - unsigned integer math.
      Sign - sign of value or result if values treated as signed.
      Overflow - equivalent of carry for signed integer math.

      And instructions to test those flags.

      If 2 8-bit numbers are added and the result is larger than
        what can fit in a 8 bit storage, the portion that can fit
        is stored and the carry flag is set.

        11111111 (255)
      + 11111111 (255)
    -----------------
     1  11111110 (510)   1 * 2^8 + 254  256+254       
 
     Code simply adds 1 to next significant byte of bytes assigned
       to store value. 
      
    Software testing carry provides "infinite range"
      But runs slower.