An arithmetic logic unit (ALU) - what is it?

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2018-03-28 03:16:11

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As you know, the computer's processor consists of four basic components: arithmetical-logical unit, module, input/output, and memory blocks and management. This architecture defined in the last century and, despite the fact that it took a long time, the classic structure of von Neumann is still relevant.

What is the ALU?

An Arithmetic logic unit – this is one of the components of the CPU, which is required for transformation of logical and arithmetic type, from basic to complex expressions. The bitness of the used operands is considered to be the word length or size.

arithmetic logic unit

The Main task of the ALU is processing the data stored in the computer's memory. In addition, the arithmetic and logic unit is capable of producing control signals which direct a computer to choose the correct way to perform the necessary computational process depending on the final data types. All operations involve electronic circuits, each of which is structurally divided into thousands of elements. Such payments are usually fast-acting and high-density.

Depending on the signals that are input, the ALU performs different types of operations with two numbers. Any arithmetic logic unit of a computer involves the implementation of four basic operations, shifts, and logical transformations. The set of operations the ALU – this is his chief characteristic.

device management

The constituent parts of the arithmetic-logic units – four main groups of nodes that correspond to management processes, transmission, storage and conversion of incoming data.

Storage Nodes ALOU

This includes:

  • Triggers, storing the auxiliary bits and the different signs of the results;
  • The registers that are responsible for the integrity of the operands, intermediate and final results.

Sometimes registers arithmetic-logic units can be combined in a dedicated memory block, and the triggers to form the status register.

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Nodes transmit ALOU

This includes:

  • Bus connecting the blocks of the device;
  • Multiplexers and gates, which is responsible for choosing the correct direction of operations.

The transform Nodes ALOU

This includes:

  • The adders performing the micro-operation;
  • A circuit performing logical operations;
  • Fingers Tinker;
  • Scissors for decimal arithmetic;
  • The code converters used for feedback or additional data;
  • Counters for counting the number of executed cycles for the implementation of auxiliary transformations.

Management Nodes ALOU

This category of objects are:

  • Control block;
  • Decoder signal;
  • The scheme of conversion of logical signs, is necessary for the formation of the branches for execution of the firmware.

Action of the control device CPU

This block is responsible for the production of a sequence of functional signals necessary for the correct execution of the specified command. As a rule, such conversions are implemented for a few bars.

The Control device provides automatic execution of the program. This enables the required branch coordinated the work of other components of the machine.

For the action of the control device corresponds to the basic principle of microprogrammable with a clear number of characteristics.

Classification ALU

Arithmetic-logic units according to the method of operating variables are divided into parallel and serial. The main difference between the ALU is the way of representation of the operands and perform operations.

The nature of the use of arithmetic-logic units are divided into a multifunctional and modular. In the ALU of the first type to perform operations with different forms of repose of the numbers are the same schemes that adapt to the requested mode data. The block devices all operations are carried out through the distribution by types of data. For actions by a decimal number, alphanumeric fields, numbers with a floating or fixed point, various schemes. Thus arithmetic logic unit operates much faster due to the parallel execution of the given task. But they have a disadvantage – increased costs of maintaining equipment.

An Arithmetic logic unit according to the method of presentation may be used:

  • Decimal numbers;
  • Floating-point;
  • Integers with a fixed point.

Device Operation

The Structure of the ALU is used to perform a logical action via functions, which are divided into the following groups:

  • Of decimal arithmetic;
  • Binary arithmetic for numbers with a clearly defined point;
  • Hexadecimal arithmetic expressions with floating delimiter;
  • Modification of the addresses of the commands;
  • Operation Boolean;
  • Convert alphanumeric fields;
  • Arithmetic.

arithmetic

Modern electronic computers are capable of implementing all of the above types of activity, and microcomputers do not have suchbasic functionality, so the most complex procedures performed through the connection of small subprograms.

Arithmetic operations and logical procedure

All actions of the ALU can be divided into several groups.

Arithmetic operations include multiplication, division, subtraction modules, the usual subtraction and addition.

the component parts of the arithmetic and logical unit

The group of logical transformations consider a Boolean “and” and “or”, that is, the conjunction and disjunction, as well as data comparison for equality. Such procedures are usually carried out over the binary words consisting of many bits.

arithmetic logic unit of a computer

The special arithmetic operations include the normalization, logical and arithmetic shifts. Among these transformations there is a significant difference. If an arithmetic shift in location, change only the digits, when the sign bit of the logical joins in the motion.

Each transaction that occurs through the use of arithmetic-logic units, can be called a sequence of Boolean functions, which describes multi-bit logic for computing machinery. For example, for binary computers use binary logic and so on, until the decimal system.

Absolutely all the arithmetic and logical transformations has its own operands, and the results output are treated as bit strings of sixteen bits. The only exceptions are the primitives of the symbolic dividing DIVS. And various flags allow to interpret the output as numbers with minus or plus overflow. Conversion logic bits is based on arithmetic modulo. The flag is placed, if there are unpredictable changes in sign. For example, adding two positive numbers, you should get the result with " + " sign. But if there is a shift in the sign bit setting unit, and the result is negative, then set the overflow flag.

structure Alu

The Logic bits of the transfer is based on unsigned arithmetic. This flag is set by the system if the generated transfer of high order cannot be written as a result. This bit of the ALU is very effective when using transformations with long-winded presentations.

Conclusion

An Arithmetic logic unit used to perform logical and arithmetic conversions on the operands necessary, which often perform the command or code numbers. After performing the operation result is re-circulated into the storage device for use in the next calculation.


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Alin Trodden - author of the article, editor
"Hi, I'm Alin Trodden. I write texts, read books, and look for impressions. And I'm not bad at telling you about it. I am always happy to participate in interesting projects."

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