Arithmetic logic unit

combinational digital circuit that performs arithmetic and bitwise operations on binary-coded integer numbers

In computing, an arithmetic logic unit (ALU) is a digital circuit that performs arithmetic and logical operations. The ALU is a basic building block of the central processing unit (CPU) of a computer, even the simplest microcontrollers contain one for purposes such as timing.

A typical schematic symbol for an ALU: A & B are the data (registers); R is the output; F is the Operand (instruction) from the Control Unit; D is an output status

Now, modern microprocessors, microcontrollers and CPUs have very powerful and very complex ALUs. Also, more recent CPUs may contain up to more than 4 ALUs (see superscalar CPUs).

Mathematician John von Neumann proposed the ALU concept in 1945.



  • Hwang, Enoch (2006). Digital Logic and Microprocessor Design with VHDL. Thomson. ISBN 0-534-46593-5.
  • Stallings, William (2006). Computer Organization & Architecture: Designing for Performance 7th ed. Pearson Prentice Hall. ISBN 0-13-185644-8.

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