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The 74181 is a 4-bit slice arithmetic logic unit (ALU), implemented as a 7400 series TTL integrated circuit. Introduced by Texas Instruments in February 1970, [ 1 ] it was the first complete ALU on a single chip. [ 2 ]
The combinational logic circuitry of the 74181 integrated circuit, an early four-bit ALU, with logic gates. An ALU is a combinational logic circuit, meaning that its outputs will change asynchronously in response to input changes.
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]
Applications such as Pinball take advantage of this to accelerate performance. The Alto has a bit-slice arithmetic logic unit (ALU) based on the Texas Instruments 74181 chip, a ROM control store with a writable control store extension and has 128 (expandable to 512) KB of main memory organized in 16-bit words.
Some models of the DEC PDP-series 'minis' used the 74181 ALU as the main computing element in the CPU. Other examples were the Data General Nova series and Hewlett-Packard 21MX, 1000, and 3000 series. In 1965, typical quantity-one pricing for the SN5400 (military grade, in ceramic welded flat-pack) was around 22 USD. [19]
A CPU built using the 74181 will use more power and dissipate more heat than any modern microprocessor of equal computing power. A CPU built using the 74181 or even faster discrete logic families (like ECL) is limited by speed of light delays inherent in the size of the chips and the spacing between them. Believe it or not, part of the reason ...
The 74181 ALU is the large IC center-right. As a demonstration of the power of their Micromatrix gate array technology, in 1968 Fairchild prototyped the 4711, a single-chip 4-bit ALU. [10] [21] The design was never intended for mass production and was quite expensive to produce.
In 1970, DG introduced the SuperNOVA, which featured a full 16-bit wide ALU using four 74181's in bit-slice fashion, and thus ran about four times as fast as the original NOVA. This was further boosted by other changes, including faster core memory and optional semiconductor memory , making the SuperNOVA the fastest mini for some time.