The ALU (Arithmetic Logic Unit) is one of the most important module in a CPU and it can be modified during most instruction executions. So more bit of operation of the ALU is important task. In this paper, 16 bit ALU is designed using VHDL and it is interfaced with RAM and ROM. This design is then implemented in Xilinx. After making an ALU, interfaced it with RAM and ROM. All results are shown as waveforms in Xilinx software. This paper helps to speed up the CPU. It can work fast and less instructions are required for the same operation compare to less bit ALU processor.