Alus

An arithmetic logic unit (ALU) is a digital circuit that performs arithmetic and logic operations on binary data. It is a core component of the central processing unit (CPU) and other digital systems. The ALU takes input operands from registers or memory, applies a function indicated by the instruction, and produces a result along with status flags.

Typical operations include addition and subtraction, multiplication and division (the latter often via iterative methods or dedicated hardware), and a set of bitwise operations such as AND, OR, XOR, and NOT. It also performs shifts and rotates and comparisons, which can set condition codes used by subsequent conditional instructions.

Architecturally, an ALU comprises one or more arithmetic circuits (adders, subtractors, multipliers) and logic circuits, sometimes with a barrel shifter and a status flag generator. Performance depends on implementation: ripple-carry adders are simple but slow, while carry-lookahead or prefix adders reduce latency. Many CPUs include fixed-width ALUs (commonly 8, 16, 32 or 64 bits); some designs reuse wider operands or support multiple precision.

In a processor, the ALU is part of the datapath and is controlled by the control unit based on the decoded instruction. Results are written back to registers, and flags indicate result properties. Floating-point operations are typically handled by a separate floating-point unit; some designs also include SIMD or multiple integer ALUs for parallel execution.

Modern processors often house several ALUs or multiple execution units to execute instructions in parallel, with pipelining and superscalar techniques. The concept of the ALU originated in early computers and remains a central term in computer architecture.