Difference between ALU and CPU


A computer comprises of several subordinate parts that contribute to the whole. Each part is responsible for specific operations and commands. The processor or Central Processing Unit (CPU), otherwise known as the brains of the computer, is the unit which is designated to interpret as well as carry out all basic operational instructions of the computer. The ALU or Arithmetic Logic Unit is a subsidiary part of the processor and carries out operations in terms of arithmetic and comparison. It is also considered to be the heart of the computer.

Comparison Chart

Expanded version Arithmetic Logic Unit Central Processing Unit
Function Carries out basic arithmetic operations, example, addition, subtraction, multiplication etc. Carries out more complicated functions of interpreting data and carrying out commands.
Designation Performs applications related to mathematics and human reasoning. Is responsible for carrying out instructions and functions on a timely basis.
Component Sub-part of the CPU Central Unit of the Computer
Known as The heart of the computer The brain of the computer

ALU (Arithmetic Logic Unit)

The Arithmetic Logic Unit or ALU is sub-alternate part of the Central Processing Unit. The primary task of this unit is to carry out operations, in relation to arithmetic logic and reasoning, such as addition, subtraction, multiplication, division and so on. It is known to be the most essential part of the CPU, and its importance is derived from the fact that many crucial operations will cease without it. The ALU, in present generation computers can be divided further into two sub-components, the AU and LU. The AU or Arithmetic Unit is in-charge of all mathematical calculations. Secondly, the LU or the Logic Unit carries out operations with regard to logical reasoning and defining the subject. Many processors are known to carry more than one AU, for processing fixed-point and floating-point operations, respectively. Floating-point operations, in certain PCs, are carried out by a separate chip known as the numeric coprocessor. The data that flows through the numeric coprocessor is direct and is directly implemented. The input of the coprocessor is usually a command word which also contains an operation mode, two or more operands and sometimes even a format code. The operation code contains instructions of what operations to perform, the operands are used in this op-code and the format code specifies whether it is a fixed point or floating point operation. The output, on the other hand, consists of a result of operations which is also recorded in a storage register. The ALU has a designated storage area for input operands, additional operands and accumulated results as well as shifted results. All the bits and operations performed flow through gated circuits into the sub units of the ALU. Overall, the ALU is a very significant part of the CPU and many critical operations would fail without it.

CPU (Central Processing Unit)

The Central Processing Unit is by far the most crucial part of the computer without which it will not function at all. Known by several other names such as brain, micro processing unit and central processor it carries out all logical operations. It resembles quite closely to the human brain in terms of functionality. The operations of the computer are carried out primarily in the CPU. The basic process of the CPU is quite simple; you enter commands by using the keyboard which is read by the CPU as binary codes (0 and 1), these instructions are sent to the registry and then interpreted and carried out by the CPU. The ALU, a sub component of the CPU as mentioned earlier, the arithmetic and logical unit. The data which the CPU receives is put through the ALU for processing. The results are then sent back to the CPU which comes out as output. The CPU also possesses a register for all storing all information sent and resends them whenever required. The L1 and L2 cache memories are two parts of the CPU which prevents loss time through re-insertion of inputs. Present generation CPUs are known to have more than one processor for faster and improved functionality. These separate processors are included in the system for faster speed and enhanced performance. In PCs these processors are in the form of integrated circuitry chips.

Key Differences

  • The Arithmetic Logic Unit performs all tasks with to human logic and arithmetic calculations whereas the Central Processing Unit carries out operations of interpreting data and giving output on time.
  • There can be more than one CPU in a single computer but there is only one ALU.
  • An ALU is a sub part of the CPU.
  • A CPU is in charge of interpreting and carrying out information fed into a computer. An ALU operates basic calculations such as addition, subtraction, multiplication etc.

Video Explanation