38 lines
1.5 KiB
Markdown
38 lines
1.5 KiB
Markdown
---
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tags: [CPU]
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---
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# Arithmetic Logic Unit (ALU)
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The ALU is the centerpiece or core of the
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[CPU](CPU_architecture.md) architecture, where the
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binary calculations occur. All the other components on the CPU chip are
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appendanges to the execution that occurs within the ALU.
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The ALU comprises
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[logic gates](Logic_gates.md) that
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execute the instructions passed from memory and where the data stored by the
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registers is acted upon. A processor's ALU is just a complex combinatorial logic
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circuit.
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It executes arithmetic and logical operations on binary numbers and where you
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will find operations conducted by
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[full-adders and half adders](Half_adder_and_full_adder.md)
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etc.
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More specifically, the ALU is responsible for the _execute_ phase of the
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[fetch, decode, execute cycle](Fetch_decode_execute.md).
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## ALU execution lifecycle
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1. **Inputs**: The ALU receives two operands and a control signal as inputs. The
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operands are the data on which the operations will be performed. The control
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signal tells the ALU which operation it needs to perform.
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2. **Perform operation**: The ALU carries out the requested operation. For
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instance, if the control signal indicates an addition operation, the ALU sums
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the two operands.
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3. **Output**: The ALU then sends the operation to another part of the CPU for
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further processing or storage. The ALU also outputs a status bit that can be
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used by other parts of the CPU to make decisions. For instance if the additon
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results in a value that is too large to be stored, the ALU will set an
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overflow flag.
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