Fetch-Decode-Execute Cycle 
See Video:	https://www.youtube.com/watch?v=XM4lGflQFvA


1	Fetch Instruction.					
	Where are the instructions stored?					
	On the hard disk. To run them, they are copied into RAM across 					
	a bus (set of wires).					
	The instruction is copied from RAM to the CPU.					
	Its copied across the data bus.					
						
2	Decode Instruction.					
	Figure out what the instruction is trying to achieve and signal					
	the circuits that do the required operation.					
	E.g					
	10001000 10010001 - what does this mean? Its machine code.					
	It means something to the machine.					
						
	e.g. it could mean add ax,bx					
	inc ax					
	sub cx,2					
						
	Decoder circuitry on the CPU does this.					
						
3	Retrieve operands (the numbers)					
	The operands can be in two places					
		-	in one of the registers e.g. ax,bx,cx,dx (16 bit)			
		        rax,rbx,rcx,rdx (64 bit)				
		-	in RAM			
	Inside the CPU the operands are copied along an internal bus					
	to the parts of the CPU that will do the addition/subtraction etc.					
						
4	Execute Instruction.					
	Circuits carry out the addition, or the subtraction or increment, or compare					
	(CMP) or whatever is required.					
						
5	Update Program Counter.					
	This is also known as the Instruction Pointer.					
	It keeps track of the next track of the next instruction to be executed.					
	Add 1 to the value in the program counter.					
	so the program counter now stores the address of the next					
	instruction to be executed.