3.1 Introduction

	The program instructions are stored in the main memory as a machine language.
	Programmers prefer to replace the binary form of the machine language to a symbolic language called
	assembly language.
	This assembly language is the tool used to use the computer architecture.
	Each computer architecture has it is own instruction sets.
	The control unit in the processor decodes the instruction and sends control signal to process it.
	To execute an instruction, the following steps are performed (Morris Mano and Charles Kime, (2007)):

		Fetch the instruction from the main memory and store it in instruction register.
		Decode the instruction.
		Locate the operands used by the instruction (if necessary).
		Fetch operands from the main memory (if necessary).
		Execute the operation.
		Store the result in the main memory or a register.
		Go back to step 1 to fetch the next instruction.

	The instruction can have different number of operands such as three-address instructions, two-address
	instructions, one-address instructions and zero-address instructions.