The arithmetic logic unit, or ALU, is the data processing unit of the microprocessor. It is the most important part of central processing unit (CPU). Functions of arithmetic logic unit (ALU) are are described below in detail:
Functions of Arithmetic Logic Unit
- Arithmetic operation (addition, subtraction, multiplication and division)
- Logical operations (OR, AND, NOT etc.)
- Decision making.
ALU is the computer’s calculator. A few current processors use multiple ALUs to attain high processing speeds. However, most microprocessors have a single ALU.
Arithmetic operations include addition, subtraction, multiplication, and division. The data operated on can be stored in various forms: the binary, BCD, EBCDIC and ASCII representations.
The ALU makes use of temporary storage areas referred to as registers. Data to be arithmetically manipulated are copied from memory and placed in registers for processing.
Upon completion of the arithmetic operation. The result can be transferred from the Accumulator to memory. The ALU uses one or more adders (shown as logic circuit) that actually add, subtract, multiply, or divided the binary digits.
Decision making is the ability to compare two numbers to determine, if the first number is smaller then, equal to, or greater than the second number and the to take appropriate action based on the result of the comparison.
For example, if the question is x > 100; the ALU would determine answer as being either true or false depending on the value of X. It is also possible to test a condition during the processing of an application and to alter the sequence of instructions accordingly.
The various circuits used in the execution of data processing instructions by a processor are usually merged into the ALU. The Complexity of an ALU is determined by the manner in which its arithmetic instructions are realized.
Simple ALUs for fixed –point operations an be constructed around the circuits developed for multiplication and division. More expensive data processing and control logic is necessary to implement floating point arithmetic in hardware.
Some microprocessor families having fixed-point ALUs employ special-purpose units called arithmetic coprocessors to perform floating- point and other complex numerical functions.
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