Consider the following datapath of a simple non-pipelined $$CPU.$$ The registers $$A,B,$$ $${A_1},{A_2},$$ $$MDR,$$ the bus and the $$ALU$$ are $$8$$-bit wide. $$SP$$ and $$MAR$$ are $$16$$-bit registers. The $$MUX$$ is of size $$8 \times \left( {2:1} \right)$$ and the $$DEMUX$$ is of size $$8 \times \left( {1:2} \right)$$. Each memory operation takes $$2$$ $$CPU$$ clock cycles and uses $$MAR$$ (Memory Address Register) and $$MDR$$ (Memory Data register). $$SP$$ can be decremented locally.

The $$CPU$$ instruction $$''push$$ $$r'',$$ where $$r=A$$ or $$B,$$ has the specification
$$\eqalign{ & \,\,\,\,\,\,\,\,\,\,\,\,\,M\left[ {SP} \right] \leftarrow r \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,SP \leftarrow SP - 1 \cr} $$
How many $$CPU$$ clock cycles are needed to execute the $$''push$$ $$r''$$ instruction?

The main difference (s) between a $$CISC$$ and a $$RISC$$ processor is/are that a $$RISC$$ processor typically: