Arithmetic Logic Unit

Arithmetic logic unit - Wikipedia, the free encyclopedia
Arithmetic logic unit. From Wikipedia, the free encyclopedia. Jump to: navigation, search ... Arithmetic logic unit (ALU) · Floating point unit (FPU) · Backside Bus ...
en.wikipedia.org

Arithmetic Logic Unit
The Central Processing Unit (CPU) Arithmetic Logic Unit ... The arithmetic logic unit performs logic functions such as AND, OR and NOT. ...
www.geocities.com

arithmetic logic unit: Information from Answers.com
(Arithmetic Logic Unit) The high-speed CPU circuit that does calculating and comparing. ... or answer questions about "arithmetic logic unit" at WikiAnswers. ...
www.answers.com

Fairchild Semiconductor Arithmetic Logic Unit (ALU)
RoHS Compliant. Arithmetic Logic Unit (ALU) (21 Matches) High Level Output Current ... Arithmetic Logic Unit (ALU) Ser Data Pol Gen/Che. Product Info. Obsolete ...
www.mouser.com

What is arithmetic-logic unit? - a definition from Whatis.com - see ...
An arithmetic-logic unit (ALU) is the part of a computer processor (CPU) that carries out arithmetic and logic operations on the operands in computer instruction words.
searchcio-midmarket.techtarget.com

54F181 - 4-Bit Arithmetic Logic Unit [Life-time buy]
... Arithmetic logic Unit (ALU) which can perform all the possible 16 logic ... 54F181 4-Bit Arithmetic Logic Unit. 218 Kbytes. 3-Dec-97. View Online. Download ...
www.national.com

Arithmetic Logic Unit
In computing, an arithmetic logic unit (ALU) is a digital circuit that performs arithmetic and logical operations. The ALU is a fundamental building block of the ...
www.geocities.com

54F181 4-Bit Arithmetic Logic Unit
The 'F181 is a 4-bit Arithmetic logic Unit (ALU) which can ... Arithmetic. Logic. Unit. Physical Dimensions. inches (millimeters) (Continued) ...
www.national.com

Arithmetic & Logic Unit IP Cores
D&R provides the world's largest directory of Arithmetic & Logic Unit IP Cores ... Subtractor > Integer, Arithmetic & Logic Unit, Coordinates Conversion, Datapath, ...
www.design-reuse.com

arothmetic logic unit
Arithmetic Logic Unit. Simple processes are performed by the Arithmetic Logic Unit (ALU for short) ... This Unit performs the fundamental arithmetic and ...
members.tripod.com

Warning: mkdir() [function.mkdir]: Permission denied in /home/webs/affiliatelib2/CacheManager.php on line 12

Warning: mkdir() [function.mkdir]: No such file or directory in /home/webs/affiliatelib2/CacheManager.php on line 12

Warning: fopen(/home/templatecore2cache//*cluesnet.com/85/856269cbca3a09c8512c446454be47213272d8c0.tc2cache) [function.fopen]: failed to open stream: No such file or directory in /home/webs/affiliatelib2/CacheManager.php on line 130

Warning: fwrite(): supplied argument is not a valid stream resource in /home/webs/affiliatelib2/CacheManager.php on line 131

Warning: fclose(): supplied argument is not a valid stream resource in /home/webs/affiliatelib2/CacheManager.php on line 132

; D is an output status

In computing, an arithmetic logic unit (ALU) 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. The processors found inside modern CPUs and Graphics processing unit have inside them very powerful and very complex ALUs; a single component may contain a number of ALUs.

Mathematician John von Neumann proposed the ALU concept in 1945, when he wrote a report on the foundations for a new computer called the EDVAC.

Early development In 1946, von Neumann worked with his colleagues in designing a computer for the Princeton Institute of Advanced Studies (IAS). The IAS computer became the prototype for many later computers. In the proposal, von Neumann outlined what he believed would be needed in his machine, including an ALU.

Von Neumann stated that an ALU is a necessity for a computer because it is guaranteed that a computer will have to compute basic mathematical operations, including addition, subtraction, multiplication, and division.Stallings page 19 He therefore believed it was "reasonable that computer should contain specialized organs for these operations."Stallings page 19

Numerical Systems An ALU must process numbers using the same format as the rest of the digital circuit. For modern processors, that almost always is the two's complement binary number representation. Early computers used a wide variety of number systems, including Signed number representations#Ones' complement, Signed number representations#Sign-and-magnitude format, and even true decimal systems, with ten tubes per digit.

ALUs for each one of these numeric systems had different designs, and that influenced the current preference for two's complement, as this is the representation that makes it easier for the ALUs to calculate additions and subtractions. Citation needed

Practical overview Most of the computer’s actions are performed by the ALU. The ALU gets data from processor registers. This data is processed and the results of this operation are stored into ALU output registers. Other mechanisms move data between these registers and memory.Stallings page 290-291

A Control Unit controls the ALU, by setting circuits that tell the ALU what operations to perform.

Simple Operations Most ALUs can perform the following operations:

Integer (computer science) arithmetic operations (addition, subtraction, and sometimes multiplication and Division (mathematics), though this is more expensive)
Bitwise operation (AND gate, NOT gate, OR gate, XOR gate)
Bitwise operation#Bit shifts operations (shifting or rotating a word by a specified number of bits to the left or right, with or without sign extension). Shifts can be interpreted as multiplications by 2 and divisions by 2.

Complex Operations An engineer can design an ALU to calculate any operation, however complicated it is; the problem is that the more complex the operation, the more expensive the ALU is, the more space it uses in the processor, and more power it dissipates, etc...

Therefore, engineers always calculate a compromise, to provide for the processor (or other circuits) an ALU powerful enough to make the processor fast, but yet not so complex as to become prohibitive. Imagine that you need to calculate, say the square root of a number; the digital engineer will examine the following options to implement this operation:

Design an extraordinarily complex ALU that calculates the square root of any number in a single step. This is called calculation in a single clock.

Design a very complex ALU that calculates the square root of any number in several steps. But, and here's the trick, that intermediate results go through a series of circuits that are arranged in a line, like a factory production line. That makes the ALU capable of accepting new numbers to calculate even before finished calculating the previous ones. That makes the ALU able to produce numbers as fast as a single-clock ALU, although the results start to flow out of the ALU only after an initial delay. This is called calculation pipeline.

Design a complex ALU that calculates the square root through several steps. This is called interactive calculation, and usually relies on control from a complex control unit with built-in microcode.

Design a simple ALU in the processor, and sell a separate specialized and costly processor that the customer can install just besides this one, and implements one of the options above. This is called the co-processor.

Tell the programmers that there is no co-processor and there is no emulation, so they will have to write their own algorithms to calculate square roots by software. This is performed by software libraries.

Emulate the existence of the co-processor, that is, whenever a program attempts to perform the square root calculation, make the processor check if there is a co-processor present and use it if there is one; if there isn't one, interrupt the processing of the program and invoke the operating system to perform the square root calculation through some software algorithm. This is called software emulation.

The options above go from the fastest and most expensive one to the slowest and least expensive one. Therefore, while even the simplest computer can calculate the most complicated formula, the simplest computers will usually take a long time doing that because several of the steps for calculating the formula.

Powerful processors like the Intel Core and AMD64 implement option #1 for several simple operations, #2 for the most common complex operations and #3 for the extremely complex operations. That is possible by the ability of building very complex ALUs in these processors.

Inputs and outputs The inputs to the ALU are the data to be operated on (called operands) and a code from the control unit indicating which operation to perform. Its output is the result of the computation.

In many designs the ALU also takes or generates as inputs or outputs a set of condition codes from or to a status register. These codes are used to indicate cases such as carry-in or carry-out, overflow, division by zero, etc.Stallings page 290-291

ALUs vs. FPUs A Floating Point Unit also performs arithmetic operations between two values, but they do so for numbers in floating point representation, which is much more complicated than the two's complement representation used in a typical ALU. In order to do these calculations, an FPU has several complex circuits built-in, including some internal ALUs.

Usually engineers call an ALU the circuit that performs arithmetic operations in integer formats (like two's complement and Binary-coded decimal), while the circuits that calculate on more complex formats like floating point, complex numbers, etc... usually receive a more illustrious name.

See also

Notes

References

External Links

A Simulator of Complex ALU in MATLAB

Arithmetic and Logic Unit from FOLDOC
Arithmetic and Logic Unit < processor > (ALU or "mill") The part of the central processing unit which performs operations such as addition, subtraction and multiplication of ...

Arithmetic logic unit - Wikipedia, the free encyclopedia
In computing, an arithmetic logic unit (ALU) is a digital circuit that performs arithmetic and logical operations. The ALU is a fundamental building block of the central processing ...

arithmetic logic unit definition of arithmetic logic unit in the Free ...
Encyclopedia article about arithmetic logic unit. Information about arithmetic logic unit in the Columbia Encyclopedia, Computer Desktop Encyclopedia, computing dictionary.

Arithmetic-logic unit definition of Arithmetic-logic unit in the Free ...
Encyclopedia article about Arithmetic-logic unit. Information about Arithmetic-logic unit in the Columbia Encyclopedia, Computer Desktop Encyclopedia, computing dictionary.

Teach ICT - arithmetic logic unit
Tons of free teaching, revision and learning material ... ALU - Arithmetic and Logic Unit . The ALU is a vital part of the central processing unit.

Arithmetic and Logic Unit
The Free Online Dictionary of Computing (http://foldoc.doc.ic.ac.uk/) is edited by Denis Howe < dbh@doc.ic.ac.uk >. Previous: ARITH-MATIC Next: arity

Arithmetic logic unit - Hutchinson encyclopedia article about ...
Hutchinson encyclopedia article about Arithmetic logic unit. Arithmetic logic unit. Information about Arithmetic logic unit in the Hutchinson encyclopedia.

Resistor and Arithmetic Logic Unit - What does RALU stand for ...
What does RALU stand for? Definition of Resistor and Arithmetic Logic Unit in the list of acronyms and abbreviations provided by the Free Online Dictionary and Thesaurus.

Arithmetic and logic unit - What does ALUN stand for? Acronyms and ...
What does ALUN stand for? Definition of Arithmetic and logic unit in the list of acronyms and abbreviations provided by the Free Online Dictionary and Thesaurus.

arithmetic and logic unit
In computing, the part of the central processing unit (CPU) that performs the basic arithmetic and logic operations on data....