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
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.
Now, modern microprocessors, microcontrollers and CPUs have very powerful and very complex ALUs. Furthermore, more recent CPUs may contain up to more than 4 ALUs (see superscalar CPUs).
Mathematician John von Neumann proposed the ALU concept in 1945.
Images for kids
A symbolic representation of an ALU and its input and output signals, indicated by arrows pointing into or out of the ALU, respectively. Each arrow represents one or more signals. Control signals enter from the left and status signals exit on the right; data flows from top to bottom.
The combinational logic circuitry of the 74181 integrated circuit, which is a simple four-bit ALU