Arithmetic logic unit: Difference between revisions

Revision as of 14:23, 14 September 2025

A symbolic representation of an ALU. The arrows represent inputs and outputs.

An 8-bit ALU with inputs A, B, !A, !B, Carry, XOR, AND, OR.

Arithmetic logic unit: In Logic World, an arithmetic logic unit (ALU) is a component of a central processor that performs basic arithmetic and logic operations.; By combining multiple operations, it is possible to perform any computation.; It may be called the "brains" of the central processor.

An ALU also has "flags" to keep track of different situations during computation. Operations that an ALU can perform include arithmetic operations such as addition and subtraction, as well as bitwise operations like XOR, NOR, AND, and OR.

The status flags it keeps track of are, for example:

A = B
A > B
A < B
Carry
Others

ALUs can have very different designs with varying specifications, such as bit size, possible operations, and speed. In principle, you don't need to implement every possible operation - a few operations are sufficient to make the system Turing complete - although additional operations make it more convenient and often faster.

Example

Below is an example of possible operations in an ALU:

Name	Opcode	Description
Add	000	Adds A and B
Sub	001	Subtracts B from A
AND	010	Outputs true if both A and B are true, otherwise false
NAND	011	Inverse of AND. If A and B are true, output is false
OR	100	Outputs true if either A or B is true
NOR	101	Inverse of OR. If either A or B is true, output is false
XOR	110	Outputs true if exactly one of A or B is true

@@ Line 1: / Line 1: @@
 [[File:ALU.gif|thumb|A symbolic representation of an ALU. The arrows represent inputs and outputs.]]
-[[File:Alu-8-bit.png|thumb|This is what a control line alu looks like it has inputs A and B, !A, !B, Carry, XOR, AND, OR.]]
+[[File:Alu-8-bit.png|thumb|An 8-bit ALU with inputs A, B, !A, !B, Carry, XOR, AND, OR.]]
-The ALU is a component in a computer that does the actal processing in a computer, it has an opcode input and inputs for A and B. Its like the brains of the computer. It can add two numbers or subtract two numbers. It can also do bitwise operations. Like XOR, NOR, AND, OR, is 0, is -, carry. It can do flags like A = B, A > B, A < B.
+{{ALU}}
+:It may be called the "brains" of the [[CPU|central processor]].
+An ALU also has "flags" to keep track of different situations during computation.
+Operations that an ALU can perform include arithmetic operations such as addition and subtraction, as well as ''bitwise'' operations like XOR, NOR, AND, and OR.
+The status flags it keeps track of are, for example:
+* ''A = B''
+* ''A > B''
+* ''A < B''
+* Carry
+* Others
+ALUs can have very different designs with varying specifications, such as bit size, possible operations, and speed. In principle, you don't need to implement every possible operation - a few operations are sufficient to make the system Turing complete - although additional operations make it more convenient and often faster.
+== Example ==
+Below is an example of possible operations in an ALU:
-Example of what opcodes may look like:
 {| class="wikitable"
-|+
+! Name
-!Name
+! Opcode
-!Opcode
+! Description
-!'''Description'''
 |-
-|Add
+| Add
-|000
+| 000
-|Adds A and B
+| Adds A and B
 |-
-|Sub
+| Sub
-|001
+| 001
-|Subtracts A and B
+| Subtracts B from A
 |-
-|AND
+| AND
-|010
+| 010
-|if A and B are true then output true else output false
+| Outputs true if both A and B are true, otherwise false
 |-
-|NAND
+| NAND
-|011
+| 011
-|invert of AND if A and B is true then output false
+| Inverse of AND. If A and B are true, output is false
 |-
-|OR
+| OR
-|100
+| 100
-|either A or B
+| Outputs true if either A or B is true
 |-
-|NOR
+| NOR
-|101
+| 101
-|invert of OR
+| Inverse of OR. If either A or B is true, output is false
 |-
-|XOR
+| XOR
-|110
+| 110
-|OR of A and B but if both are true then output false
+| Outputs true if exactly one of A or B is true
 |}