I. INTRODUCTIONA processor is a main element of any digital system. And an ALU is one of the main components of a microprocessor. To give a simple analogy, CPU works like a brain for any system and ALU works like a brain for the CPU. So it's a computer brain brain. They are made of fast dynamic logic circuits and have carefully optimized structures. Of the total power consumption of any processor, the CPU accounts for a significant portion. The ALU also contributes to one of the highest power density slots in the processor because it is clocked at the highest speed and is busy almost all the time, resulting in thermal hot spots and power gradients. pronounced temperature within the execution core. Therefore, this strongly motivates us for energy-efficient ALU designs that meet high performance requirements, while reducing peak and average power dissipation.[1,2] Basically, ALU is a combinational circuit that performs arithmetic operations and logic on a pair of n-bit operands, for example A [0:7] and B [0:7] for 8 bits. The typical internal structure of an 8-bit ALU is shown in Fig.1. The architecture can be modified in the same way for the lower bits. Our work is divided into following sections: Section (II) gives a description of various units and operations of the ALU, Section (III) briefly presents the design of various components of the ALU such as Shifter, Adder , the subtractor, etc. using a conventional complementary design. Section (IV) presents the GDI technique. Section (V) presents simulation results and performance analysis of various ALU blocks with complementary and GDI techniques and comparison of their performance and optimized area. Finally, the work is concluded in section (VI)II. ARITHMETIC LOGIC UNITArithmetic Unit 2.1Employment of ad...... middle of paper ......egy for Barrel Shifter using Mux at 180nm technology node", International Journal of Science and Modern Engineering (IJISME) , ISSN: 2319-6386, Volume-1, Issue-8, July 2013[8] Arun Prakash Singh, Rohit Kumar, “Implementation of 1-bit full adder using gate diffusion input (GDI) cell” , International Journal of Electronics and Computer Science Engineering, ISSN-2277-1956/V1N2-333-342[9] Arkadiy Morgenshtein, Alexander Fish, and Israel A. Wagner, “Gate Diffusion Input (GDI): An Energy-Efficient Method for digital combinational circuits”, IEEE Transactions On Very Large Scale Integration (VLSI) Systems, Vol. 10, No. 5, October 2002[10] Hamid Reza Naghizadeh, Mohammad Sarvghad Moghadam, Saber Izadpanah Tous and Abbas Golmakani, “Design of two high-performance 1-bit CMOS full-add cells”, International Journal of Computing and Digital Systems 2, No. 1, 47-52 (2013)