Calculating is manipulating numbers. It may be done manually on pen and pare, on the computer, or on a traditional calculator.
natural numbers are used in real life for counting, adding, subtracting and even for calculting money purposes
It contains an address, which will be used in calculting the actual address of an operand. Example (Sytem/360): L R2,12(R3,R4) meaning: tempadd := 12 + R3 + R4 R2 := content of memory at tempadd here R3 is called base registed, R4 is called index register. Or vice versa.