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The 74S181 4-bit ALU bitslice resting on a page from the datasheet.

The 74181 is a bit slice arithmetic logic unit (ALU), implemented as a 7400 series TTL integrated circuit. The first complete ALU on a single chip,<ref>'Computer Structures: Principles and Examples' C. Gordon Bell page 63: "The earliest and most famous chip, the 74181 arithmetic logic unit (ALU), provided up to 32 functions of two 4-bit variables."</ref> it was used as the arithmetic/logic core in the CPUs of many historically significant minicomputers and other devices.

The 74181 represents an evolutionary step between the CPUs of the 1960s, which were constructed using discrete logic gates, and today's single-chip CPUs or microprocessors. Although no longer used in commercial products, the 74181 is still referenced in computer organization textbooks and technical papers. It is also sometimes used in 'hands-on' college courses, to train future computer architects.

74181 sections
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