The
74181 is a
bit sliceBit slicing is a technique for constructing a processor from modules of smaller bit width. Each of these components processes one bit field or "slice" of an operand. The grouped processing components would then have the capability to process the chosen full word-length of a particular software design...
arithmetic logic unitIn computing, an arithmetic logic unit is a digital circuit that performs arithmetic and logical operations. The ALU is a fundamental building block of the central processing unit of a computer, and even the simplest microprocessors contain one for purposes such as maintaining timers...
(ALU), implemented as a
7400 seriesThe 7400 series of Transistor-transistor logic integrated circuits are historically important as the first widespread family of TTL integrated circuit logic . It was used to build the mini and mainframe computers of the 1960s and 1970s...
TTL
integrated circuitIn electronics, an integrated circuit is a miniaturized electronic circuit that has been manufactured in the surface of a thin substrate of semiconductor material...
. The first complete ALU on a single chip, 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 gateA logic gate performs a logical operation on one or more logic inputs and produces a single logic output. The logic normally performed is Boolean logic and is most commonly found in digital circuits...
s, and today's single-chip CPUs or
microprocessorA microprocessor incorporates most or all of the functions of a central processing unit on a single integrated circuit . The first microprocessors emerged in the early 1970s and were used for electronic calculators, using binary-coded decimal arithmetic on 4-bit words...
s.
The
74181 is a
bit sliceBit slicing is a technique for constructing a processor from modules of smaller bit width. Each of these components processes one bit field or "slice" of an operand. The grouped processing components would then have the capability to process the chosen full word-length of a particular software design...
arithmetic logic unitIn computing, an arithmetic logic unit is a digital circuit that performs arithmetic and logical operations. The ALU is a fundamental building block of the central processing unit of a computer, and even the simplest microprocessors contain one for purposes such as maintaining timers...
(ALU), implemented as a
7400 seriesThe 7400 series of Transistor-transistor logic integrated circuits are historically important as the first widespread family of TTL integrated circuit logic . It was used to build the mini and mainframe computers of the 1960s and 1970s...
TTL
integrated circuitIn electronics, an integrated circuit is a miniaturized electronic circuit that has been manufactured in the surface of a thin substrate of semiconductor material...
. The first complete ALU on a single chip, 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 gateA logic gate performs a logical operation on one or more logic inputs and produces a single logic output. The logic normally performed is Boolean logic and is most commonly found in digital circuits...
s, and today's single-chip CPUs or
microprocessorA microprocessor incorporates most or all of the functions of a central processing unit on a single integrated circuit . The first microprocessors emerged in the early 1970s and were used for electronic calculators, using binary-coded decimal arithmetic on 4-bit words...
s. Although no longer used in commercial products, the '181 is still referenced in computer organization textbooks and technical papers. It is also sometimes used in 'hands-on' college courses, to train future
computer architectsCPU design is the design engineering task of creating a central processing unit , a component of computer hardware. It is a subfield of electronics engineering and computer engineering.- Overview :CPU design focuses on these areas:...
.
Specifications
The 74181 is a
7400 seriesThe 7400 series of Transistor-transistor logic integrated circuits are historically important as the first widespread family of TTL integrated circuit logic . It was used to build the mini and mainframe computers of the 1960s and 1970s...
medium-scale integration (MSI) TTL
integrated circuitIn electronics, an integrated circuit is a miniaturized electronic circuit that has been manufactured in the surface of a thin substrate of semiconductor material...
, containing the equivalent of 75 logic gates and most commonly packaged as a 24-pin
DIPIn microelectronics, a dual in-line package , sometimes called a DIL package, is an electronic device package with a rectangular housing and two parallel rows of electrical connecting pins. The pins are all parallel, point downward, and extend past the bottom plane of the package at least enough...
. The 4-bit wide ALU can perform all the traditional add / subtract / decrement operations with or without carry, as well as
ANDThe AND gate is a digital logic gate that implements logical conjunction - it behaves according to the truth table to the right. A HIGH output results only if both the inputs to the AND gate are HIGH . If neither or only one input to the AND gate is HIGH, a LOW output results...
/ NAND,
ORPRASADThe OR gate is a digital logic gate that implements logical disjunction - it behaves according to the truth table to the right. A HIGH output results if one or both the inputs to the gate are HIGH . If neither input is HIGH, a LOW output results...
/ NOR, XOR, and
shiftIn digital circuits, a shift register is a cascade of flip flops, sharing the same clock, which has the output of any one but the last flip-flop connected to the "data" input of the next one in the chain, resulting in a circuit that shifts by one position the one-dimensional "bit array" stored in...
. Many variations of these basic functions are available, for a total of 16 arithmetic and 16 logical operations on two four bit words. Multiply and divide functions are not provided but can be performed in multiple steps using the shift and add or subtract functions.
The 74181 performs these operations on two four bit operands generating a four bit result with carry in 22 nanoseconds. The 74S181 performs the same operations in 11 nanoseconds, while the 74F181 performs the operations in 7 nanoseconds (typical).
Multiple 'slices' can be combined for arbitrarily large word sizes. For example, sixteen 74S181s and five 74S182 look ahead carry generators can be combined to perform the same operations on 64-bit operands in 28 nanoseconds. Although overshadowed by the performance of today's multi-gigahertz 64-bit microprocessors, this was quite impressive when compared to the sub megahertz clock speeds of the early four and eight bit microprocessors.
Significance
Although the 74181 is only an
ALUIn computing, an arithmetic logic unit is a digital circuit that performs arithmetic and logical operations. The ALU is a fundamental building block of the central processing unit of a computer, and even the simplest microprocessors contain one for purposes such as maintaining timers...
and not a complete
microprocessorA microprocessor incorporates most or all of the functions of a central processing unit on a single integrated circuit . The first microprocessors emerged in the early 1970s and were used for electronic calculators, using binary-coded decimal arithmetic on 4-bit words...
it greatly simplified the development and manufacture of computers and other devices that required high speed computation during the late 1960s through the early 1980s, and is still referenced as a "classic" ALU design.
Prior to the introduction of the 74181, computer CPUs occupied multiple circuit boards and even very simple computers could fill multiple cabinets. The '181 allowed an entire CPU and in some cases, an entire computer to be constructed on a single large
printed circuit boardA printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, or traces, etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring board...
. The '181 occupies a historically significant stage between older CPUs based on discrete logic functions spread over multiple circuit boards and modern microprocessors that incorporate all CPU functions in a single component. The '181 was used in various minicomputers and other devices beginning in the late 1960s, but as microprocessors became more powerful the practice of building a CPU from discrete components fell out of favor and the 74181 was not used in any new designs.
Today
CPU designs based on the 74181 are not commercially viable today due the comparatively low price and high performance of microprocessors. However, the 74181 is still of interest in the teaching of computer organization and
CPU designCPU design is the design engineering task of creating a central processing unit , a component of computer hardware. It is a subfield of electronics engineering and computer engineering.- Overview :CPU design focuses on these areas:...
because it provides opportunities for hands-on design and experimentation that are rarely available to students.
Computers
Many computer CPUs and subsystems were based on the '181, including several historically significant models.
- NOVA
The Data General Nova was a popular 16-bit minicomputer built by the United States company Data General starting in 1969. The Nova was packaged into a single rack mount case and had enough power to do most simple computing tasks. The Nova became popular in science laboratories around the world, and...
- First widely available 16-bit minicomputerA minicomputer is a class of multi-user computers that lies in the middle range of the computing spectrum, in between the largest multi-user systems and the smallest single-user systems...
manufactured by Data GeneralData General was one of the first minicomputer firms from the late 1960s. Three of the four founders were former employees of Digital Equipment Corporation. Their first product, the Nova, was a 16-bit minicomputer. This was followed by the Supernova and Eclipse product lines, all of which were...
. This was the first design (in 1968) to use the 74181
- PDP-11
The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corp. from 1970 into the 1990s. Though not explicitly conceived as successor to DEC's PDP-8 computer in the PDP series of computers , the PDP-11 replaced the PDP-8 in many real-time applications...
- Most popular minicomputer of all time, manufactured by Digital Equipment CorporationDigital Equipment Corporation was a pioneering American company in the computer industry. It is often referred to within the computing industry as DEC...
.
- Xerox Alto
The Xerox Alto was an early personal computer developed at Xerox PARC in 1973. It was the first computer to use the desktop metaphor and graphical user interface ....
- The first computer to use the desktop metaphor and graphical user interface (GUI).
- VAX-11/780 - The first VAX
VAX was an instruction set architecture developed by Digital Equipment Corporation in the mid-1970s. A 32-bit complex instruction set computer ISA, it was designed to extend or replace DEC's various Programmed Data Processor ISAs...
, the most popular 32-bit computer of the 1980s manufactured by Digital Equipment Corp.
- Three Rivers PERQ, a commercial computer workstation based on the Xerox Alto and first released in 1979.
- KMC11 - Peripheral processor for Digital Equipment Corporation
Digital Equipment Corporation was a pioneering American company in the computer industry. It is often referred to within the computing industry as DEC...
PDP-11The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corp. from 1970 into the 1990s. Though not explicitly conceived as successor to DEC's PDP-8 computer in the PDP series of computers , the PDP-11 replaced the PDP-8 in many real-time applications...
.
- FPP-12 - Floating point unit for the Digital Equipment Corp. PDP-12.
- Wang 2200
Wang's first minicomputer which could perform data processing in a common computer language was the Wang 2200 which appeared in May 1973. Unlike some other desktop computers such as the HP 9830, it had a CRT in a cabinet that also included an integrated computer controlled cassette tape storage...
CPU (one 74181 per CPU) and disk controller (2 74181s per controller)
Other uses
- Vectorbeam
Vectorbeam was an arcade game manufacturer active in the late 1970s who specialized in vector graphics-based arcade games. It was formed after splitting off from its primary competitor, Cinematronics, and disappeared after re-merging with them soon after....
- Arcade gameAn arcade game is a coin-operated entertainment machine, typically installed in businesses such as restaurants, public houses, video arcades, and Family Entertainment Centers...
platformThe word platform is used in several different contexts, usually referring to some kind of standing surface used to support things, give them stability, or visibility:* Railway platform, an area at a train station to alight from/embark on trains or trams...
used by CinematronicsCinematronics Incorporated was a pioneering arcade game developer that had its heyday in the era of vector display games. While other companies released games based on raster displays, early in their history, Cinematronics and Atari released vector-display games, which offered a distinctive look...
for various arcade games including Space WarsSpace Wars was the first vector graphics arcade game. It is based on Spacewar!, a PDP-1 program that might arguably be the earliest computer game.-Description:...
, Starhawk, WarriorWarrior is a 1979 arcade game and is one of the pioneers in the fighting game genre. It has been regarded as the first fighting game, however it was predated by Sega's Heavyweight Champ, released in 1976....
, Star CastleStar Castle is a 1980 vector arcade game by Cinematronics. The game involves obliterating a series of defenses circumferencing a stationary turret in the center of the screen. The game was designed by Tim Skelly and programmed by Scott Boden. Tim Skelly also created a number of other...
and others.
External links
Manufacturer's data sheets: