Arithmetic logic unit

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. 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.

Arithmetic Logic Unit Media

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, an early four-bit ALU
Logical and arithmetic rotate one bit left
Rotate right arithmetically
Logical and arithmetic rotate one bit left
Logical rotate one bit right
Rotate one bit left
Rotate one bit right
Rotate one bit left through the carry bit
Rotate right through carry