Recall the basic cpu architecture given in the book and presented in class. as a reminder, the cpu has a pc, ir, and an ac register. you can assume that the pc and ac registers will be initialized to zero when the cpu starts. each instruction is 16 bits long. the first four bits form the opcode, and the rest of the bits form an address to a memory location. there will be a total of 16 (24 ) instructions for this architecture. list eight instructions (not given in the book) for this cpu, and for each instruction, explain what it does and why you feel it is necessary or useful to have it.