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In computing, an arithmetic logic unit (ALU) is a combinational digital circuit that performs arithmetic and bitwise operations on integer binary numbers. [ 1 ] [ 2 ] This is in contrast to a floating-point unit (FPU), which operates on floating point numbers.
The 74181 implements all 16 possible logical functions with two variables. Its arithmetic functions include addition and subtraction with and without carry. It can be used with active-high data, in which a high logic level corresponds to 1, and active-low data, in which a low logic level corresponds to 1. [4]
A data path is a collection of functional units such as arithmetic logic units (ALUs) or multipliers that perform data processing operations, registers, and buses. [1] Along with the control unit it composes the central processing unit (CPU). [1] A larger data path can be made by joining more than one data paths using multiplexers.
In many computers and other kinds of processors, adders are used in the arithmetic logic units (ALUs). They are also used in other parts of the processor, where they are used to calculate addresses , table indices , increment and decrement operators and similar operations.
Adders are a part of the core of an arithmetic logic unit (ALU). The control unit decides which operations an ALU should perform (based on the op code being executed) and sets the ALU operation. The D input to the adder–subtractor above would be one such control line from the control unit.
In the 1970s and 1980s, a number of research and commercial computers used bit slicing, in which the CPU's arithmetic logic unit (ALU) was built from multiple 4-bit-wide sections, each section including a chip such as an Am2901 or 74181. The Zilog Z80, although it is an 8-bit microprocessor, has a 4-bit ALU. [11] [12]
The control unit (CU) is a component of a computer's central processing unit (CPU) that directs the operation of the processor. A CU typically uses a binary decoder to convert coded instructions into timing and control signals that direct the operation of the other units (memory, arithmetic logic unit and input and output devices, etc.).
For example, the part of an arithmetic logic unit, or ALU, that does mathematical calculations is constructed using combinational logic. Other circuits used in computers, such as half adders, full adders, half subtractors, full subtractors, multiplexers, demultiplexers, encoders and decoders are also made by using combinational logic.