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Arithmetic Logic Unit (ALU)

Definition - What does Arithmetic Logic Unit (ALU) mean?

An arithmetic logic unit (ALU) is a major component of the central processing unit of a computer system. It does all processes related to arithmetic and logic operations that need to be done on instruction words. In some microprocessor architectures, the ALU is divided into the arithmetic unit (AU) and the logic unit (LU).

An ALU can be designed by engineers to calculate any operation. As the operations become more complex, the ALU also becomes more expensive, takes up more space in the CPU and dissipates more heat. That is why engineers make the ALU powerful enough to ensure that the CPU is also powerful and fast, but not so complex as to become prohibitive in terms of cost and other disadvantages.

An arithmetic logic unit is also known as an integer unit (IU).

Techopedia explains Arithmetic Logic Unit (ALU)

The arithmetic logic unit is that part of the CPU that handles all the calculations the CPU may need. Most of these operations are logical in nature. Depending on how the ALU is designed, it can make the CPU more powerful, but it also consumes more energy and creates more heat. Therefore, there must be a balance between how powerful and complex the ALU is and how expensive the whole unit becomes. This is why faster CPUs are more expensive, consume more power and dissipate more heat.

The main functions of the ALU are to do arithmetic and logic operations, including bit shifting operations. These are essential processes that need to be done on almost any data that is being processed by the CPU.

ALUs routinely perform the following operations:

  • Logical Operations: These include AND, OR, NOT, XOR, NOR, NAND, etc.
  • Bit-Shifting Operations: This pertains to shifting the positions of the bits by a certain number of places to the right or left, which is considered a multiplication operation.
  • Arithmetic Operations: This refers to bit addition and subtraction. Although multiplication and division are sometimes used, these operations are more expensive to make. Addition can be used to substitute for multiplication and subtraction for division.
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