Arithmetic logic unit - Revision history

FoxFireFive at 19:44, 14 March 2026

2026-03-14T19:44:38Z

← Older revision		Revision as of 19:44, 14 March 2026
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	{{Stub}}[[File:ALU.gif\|thumb\|A symbolic representation of an ALU. The arrows represent inputs and outputs.]]		{{Stub}}[[File:ALU.gif\|thumb\|A symbolic representation of an ALU. The arrows represent inputs and outputs.]]
	[[File:Alu-8-bit.png\|thumb\|An 8-bit ALU with inputs A, B, !A, !B, Carry, XOR, AND, OR.]]An Arithmetic Logic Unit (ALU) is a circuit that performs basic arithmetic and logic operations, ~~usually~~ used in CPUs. They usually have "flags" to keep track of different things during execution, like if the result overflowed, or the result was zero. Flags are usually implemented with flip-flops. Operations that an ALU ~~can~~ perform ~~include~~ arithmetic operations such as addition and subtraction, as well as bitwise operations like XOR, AND, and OR.		[[File:Alu-8-bit.png\|thumb\|An 8-bit ALU with inputs A, B, !A, !B, Carry, XOR, AND, OR.]]An Arithmetic Logic Unit (ALU) is a circuit that performs basic arithmetic and logic operations, often used in CPUs. They usually have "flags" to keep track of different things during execution, like if the result overflowed, or the result was zero. Flags are usually implemented with flip-flops. Operations that an ALU could perform are arithmetic operations such as addition and subtraction, as well as bitwise operations like XOR, AND, and OR.

	The different kinds of flags an ALU could keep track of are:		The different kinds of flags an ALU could keep track of are:
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	\| Outputs true if exactly one of A or B is true		\| Outputs true if exactly one of A or B is true
	\|}		\|}
	{{Todo\|Improve this section, without ai.		If your ALU only has arithmatic functions, it would be an Arithmatic Unit (AU). If your ALU only has logic functions, it would be a Logic Unit (LU).
	~~man I am so tired its 6:18am and i just want to go to bed~~.}}		{{Todo\|Improve this section, without ai.}}

	== Multiplexer based ALU's ==		== Multiplexer based ALU's ==

FoxFireFive: Fixed the article by mostly re-writting it. PLEASE STOP USING AI FOR THE LOVE OF ALL THAT'S HOLY. IF YOU CAN'T EDIT WITHOUT AI, DON'T EDIT!!

2026-03-14T10:21:10Z

Fixed the article by mostly re-writting it. PLEASE STOP USING AI FOR THE LOVE OF ALL THAT'S HOLY. IF YOU CAN'T EDIT WITHOUT AI, DON'T EDIT!!

Show changes

Rgjava at 04:13, 19 December 2025

2025-12-19T04:13:24Z

← Older revision		Revision as of 04:13, 19 December 2025
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	* NOR		* NOR

	They can do lots of operations. ~~they~~ don't have a sub mode input ~~insread to subtract number~~ you can turn on invert B (!B) and carry.		They can do lots of operations. They don't have a sub mode input, instead you can turn on invert B (!B) and carry to preform subtraction.

	Note they don't have opcode input like mux based alus so you have to make a ROM that turns on specific pins like:		Note they don't have opcode input like mux based alus so you have to make a ROM that turns on specific pins like:
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	Pros:		Pros:

	* They allow for complex ~~oprations~~.		* They allow for complex operations.
	* They are small		* They are small

Rgjava: Fixed grammer mystakes.

2025-12-19T04:10:08Z

Fixed grammer mystakes.

← Older revision		Revision as of 04:10, 19 December 2025
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	=== Mux Based ALU's ===		=== Mux Based ALU's ===
	[[File:Muxbased alu.jpg\|thumb\|266x266px\|Simple Mux Based ALU]]		[[File:Muxbased alu.jpg\|thumb\|266x266px\|Simple Mux Based ALU]]
	Mux based ALU's uses a [[Multiplexer]] to select outputs from gates or ~~oprations~~		Mux based ALU's uses a [[Multiplexer]] to select outputs from gates or operations

	Pros:		Pros:
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	Cons:		Cons:

	* They take up ~~alot~~ of space		* They take up a lot of space
	* They are limited in operations		* They are limited in operations

	=== Control Line Based ALU's ===		=== Control Line Based ALU's ===
	Unlike Mux Based ALU's, Control Line Based ALU's ~~dont~~ have a mux instead they have inputs like:		Unlike Mux Based ALU's, Control Line Based ALU's don't have a mux instead they have inputs like:

	* Carry		* Carry
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	* NOR		* NOR

	They can do lots of operations. they ~~dont~~ have a sub ~~mod~~ input insread to subtract number you can turn on invert B (!B) and carry.		They can do lots of operations. they don't have a sub mode input insread to subtract number you can turn on invert B (!B) and carry.

	Note they ~~dont~~ have opcode input like mux based alus so you have to make a ROM that turns on specific pins like:		Note they don't have opcode input like mux based alus so you have to make a ROM that turns on specific pins like:
	{\| class="wikitable"		{\| class="wikitable"
	\|+		\|+

Rgjava: Fixed grammer mystakes.

2025-09-14T15:45:56Z

Fixed grammer mystakes.

← Older revision		Revision as of 15:45, 14 September 2025
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	[[File:Muxbased alu.jpg\|thumb\|266x266px\|Simple Mux Based ALU]]		[[File:Muxbased alu.jpg\|thumb\|266x266px\|Simple Mux Based ALU]]
	Mux based ALU's uses a [[Multiplexer]] to select outputs from gates or oprations		Mux based ALU's uses a [[Multiplexer]] to select outputs from gates or oprations

	Pros:		Pros:

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	* They take up alot of space		* They take up alot of space
	* They are limited in ~~oprations~~		* They are limited in operations

	=== Control Line Based ALU's ===		=== Control Line Based ALU's ===
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	* NOR		* NOR

	They can do lots of ~~oprations~~. they dont have a sub mod input insread to subtract number you can turn on invert B (!B) and carry.		They can do lots of operations. they dont have a sub mod input insread to subtract number you can turn on invert B (!B) and carry.

	Note they dont have opcode input like mux based alus so you have to make a ROM that turns on specific pins like:		Note they dont have opcode input like mux based alus so you have to make a ROM that turns on specific pins like:
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	\|Decrements A by 1		\|Decrements A by 1
	\|}		\|}
			Pros:

			* They allow for complex oprations.
			* They are small

			Cons:

			* They are complex

Rgjava: added Mux based alus and control Line based alu's.

2025-09-14T15:41:26Z

added Mux based alus and control Line based alu's.

@@ Line 56: / Line 56: @@
 * Mux Based ALU's
-* Control Line based ALU's
+* Control Line Based ALU's
-[[Multiplexer|Multiplexer]]
+=== Mux Based ALU's ===

Rgjava: /* ALU Designs */

2025-09-14T15:15:38Z

ALU Designs

← Older revision		Revision as of 15:15, 14 September 2025
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	== ALU Designs ==		== ALU Designs ==
	Their are two main alu Designs:		Their are two main alu Designs:

			* Mux Based ALU's
			* Control Line based ALU's
			[[Multiplexer\|Multiplexer]]

Rgjava at 15:10, 14 September 2025

2025-09-14T15:10:28Z

← Older revision		Revision as of 15:10, 14 September 2025
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	\| Outputs true if exactly one of A or B is true		\| Outputs true if exactly one of A or B is true
	\|}		\|}
			== ALU Designs ==
			Their are two main alu Designs:

DjSapsan: Tweaks to the article

2025-09-14T14:23:01Z

Tweaks to the article

← Older revision		Revision as of 14:23, 14 September 2025
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	[[File:ALU.gif\|thumb\|A symbolic representation of an ALU. The arrows represent inputs and outputs.]]		[[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"		{\| 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
	\|}		\|}

Rgjava: added the alu example. :3

2025-09-14T13:46:55Z

added the alu example. :3

← Older revision		Revision as of 13:46, 14 September 2025
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	[[File:ALU.gif\|thumb\|A symbolic representation of an ALU. The arrows represent inputs and outputs.]]		[[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.]]
	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.		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.