74181
Encyclopedia
Bit slicing
Bit 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...
arithmetic logic unit
Arithmetic logic unit
In 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 series
7400 series
The 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 circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into 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 gate
Logic gate
A logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and...
s, and today's single-chip CPUs or microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
s. 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
CPU design
CPU 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 series7400 series
The 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 circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
, containing the equivalent of 75 logic gates and most commonly packaged as a 24-pin DIP
Dual in-line package
In microelectronics, a dual in-line package is an electronic device package with a rectangular housing and two parallel rows of electrical connecting pins. The package may be through-hole mounted to a printed circuit board or inserted in a socket.A DIP is usually referred to as a DIPn, where n is...
. The 4-bit wide ALU can perform all the traditional add / subtract / decrement operations with or without carry, as well as AND
AND gate
The AND gate is a basic 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, OR
OR gate
The 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 shift
Shift register
In 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. Shift is not an explicit function but can be derived from several available functions including (A+B) plus A, A plus AB.
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 ALUArithmetic logic unit
In 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 microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
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 74181 allowed an entire CPU and in some cases, an entire computer to be constructed on a single large printed circuit board
Printed circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
. The 74181 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 74181 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
CPU 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.
- Digital Electronics with VHDL (Quartus II Version) review in Journal of Modern Engineering, Volume 7, Number 2, Spring 2007.
- A Minimal TTL Processor for Architecture Exploration a paper describing how the 74181 can be used to teach CPU architecture.
- A Hardware Lab for the Computer Organization Course at Small Colleges - Another example of how the 74181 is used today in a teaching environment.
- 74181 + 74182 demonstration Java - based simulator
Computers
Many computer CPUs and subsystems were based on the 74181, including several historically significant models.- NOVAData General NovaThe Data General Nova was a popular 16-bit minicomputer built by the American 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 minicomputerMinicomputerA 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 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 Data General Nova, was a 16-bit minicomputer...
. This was the first design (in 1968) to use the 74181 - PDP-11PDP-11The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years...
- Most popular minicomputer of all time, manufactured by Digital Equipment CorporationDigital Equipment CorporationDigital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
. - Xerox AltoXerox AltoThe Xerox Alto was one of the first computers designed for individual use , making it arguably what is now called a personal computer. It was developed at Xerox PARC in 1973...
- The first computer to use the desktop metaphor and graphical user interface (GUI). - VAX-11/780 - The first VAXVAXVAX 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.
- Computer Automation, a computer that found use in LSI IC test equipment and process control.
- KMC11 - Peripheral processor for Digital Equipment CorporationDigital Equipment CorporationDigital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
PDP-11PDP-11The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years...
. - FPP-12 - Floating point unit for the Digital Equipment Corp. PDP-12.
- Wang 2200Wang 2200Wang 2200, appeared in May 1973, was Wang Laboratories' first minicomputer that could perform data processing in a common computer language. Unlike some other desktop computers, such as the HP 9830, it had a cathode ray tube in a cabinet that also included an integrated computer controlled...
CPU (one 74181 per CPU) and disk controller (2 74181s per controller)
Other uses
- VectorbeamVectorbeamVectorbeam 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 gameArcade gameAn arcade game is a coin-operated entertainment machine, usually installed in public businesses such as restaurants, bars, and amusement arcades. Most arcade games are video games, pinball machines, electro-mechanical games, redemption games, and merchandisers...
platform used by CinematronicsCinematronicsCinematronics 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 WarsSpace Wars was the first vector graphics arcade game. It is based on Spacewar!, a PDP-1 program. It was ported to the Vectrex in 1982...
, Starhawk, WarriorWarrior (arcade game)Warrior 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 CastleStar Castle is a 1980 vector arcade game by Cinematronics. The game involves obliterating a series of defenses orbiting 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 Cinematronics...
and others.