Browse Definitions:
Definition

logic gate (AND, OR, XOR, NOT, NAND, NOR and XNOR)

AND | OR | XOR | NOT | NAND | NOR | XNOR

A logic gate is an elementary building block of a digital circuit. Most logic gates have two inputs and one output. At any given moment, every terminal is in one of the two binary conditions low (0) or high (1), represented by different voltage levels. The logic state of a terminal can, and generally does, change often, as the circuit processes data. In most logic gates, the low state is approximately zero volts (0 V), while the high state is approximately five volts positive (+5 V).

There are seven basic logic gates: AND, OR, XOR, NOT, NAND, NOR, and XNOR.

The AND gate is so named because, if 0 is called "false" and 1 is called "true," the gate acts in the same way as the logical "and" operator. The following illustration and table show the circuit symbol and logic combinations for an AND gate. (In the symbol, the input terminals are at left and the output terminal is at right.) The output is "true" when both inputs are "true." Otherwise, the output is "false."

/WhatIs/images/and.gif (220 bytes)

AND gate

Input 1 Input 2 Output
     
  1  
1    
1 1 1

The OR gate gets its name from the fact that it behaves after the fashion of the logical inclusive "or." The output is "true" if either or both of the inputs are "true." If both inputs are "false," then the output is "false."

/WhatIs/images/or.gif (224 bytes)

OR gate


Input 1 Input 2 Output
     
  1 1
1   1
1 1 1

 

The XOR ( exclusive-OR ) gate acts in the same way as the logical "either/or." The output is "true" if either, but not both, of the inputs are "true." The output is "false" if both inputs are "false" or if both inputs are "true." Another way of looking at this circuit is to observe that the output is 1 if the inputs are different, but 0 if the inputs are the same.

 

XOR gate

Input 1 Input 2 Output
     
  1 1
1   1
1 1  

 

A logical inverter , sometimes called a NOT gate to differentiate it from other types of electronic inverter devices, has only one input. It reverses the logic state.

 

/WhatIs/images/not.gif (240 bytes)

 

Inverter or NOT gate
Input Output
1  
  1

 

The NAND gate operates as an AND gate followed by a NOT gate. It acts in the manner of the logical operation "and" followed by negation. The output is "false" if both inputs are "true." Otherwise, the output is "true."

/WhatIs/images/nand.gif (240 bytes)

NAND gate

Input 1 Input 2 Output
    1
  1 1
1   1
1 1  

 

The NOR gate is a combination OR gate followed by an inverter. Its output is "true" if both inputs are "false." Otherwise, the output is "false."

/WhatIs/images/nor.gif (237 bytes)

NOR gate

Input 1 Input 2 Output
    1
  1  
1    
1 1  

 

The XNOR (exclusive-NOR) gate is a combination XOR gate followed by an inverter. Its output is "true" if the inputs are the same, and"false" if the inputs are different.

/WhatIs/images/xnor.gif (278 bytes)

XNOR gate

Input 1 Input 2 Output
    1
  1  
1    
1 1 1

Using combinations of logic gates, complex operations can be performed. In theory, there is no limit to the number of gates that can be arrayed together in a single device. But in practice, there is a limit to the number of gates that can be packed into a given physical space. Arrays of logic gates are found in digital integrated circuits (ICs). As IC technology advances, the required physical volume for each individual logic gate decreases and digital devices of the same or smaller size become capable of performing ever-more-complicated operations at ever-increasing speeds.

See an introductory tutorial on logic gates:

 

This was last updated in May 2015

Continue Reading About logic gate (AND, OR, XOR, NOT, NAND, NOR and XNOR)

Join the conversation

18 comments

Send me notifications when other members comment.

By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy

Please create a username to comment.

there are only three basic gates AND OR NOT
Universal Gates are NAND NOR
Derrived gates are XOR XNOR
Cancel
What do thou mean good sir?
Cancel
it is not given a full part just basic is here
Cancel
WHY ARE THE NAMES OF LOGIC GATES ALL CAPITAL LETTERS??
Cancel
Because if i was to call an and gate an and gate or an or gate an or gate it would look confusing
Cancel
i still don't get it! :(
Cancel
Easy, a great refresher. This is basic. The diagrams help the most.
Cancel
can you post the gate transformation next time.

but thanks a lot,
Cancel
where is the memory cell gate?
Cancel
its nice ,i like it
Cancel
Thank you! Only thing I found that actually makes sense.
Cancel
This is very useful...
William
Chary
Rachel VO
Cancel
Please note that there are no 7 basic gates but there are ONLY and ONLY 2 basic gates that are AND and OR and an INVERTER with using AND, OR and INVERTOR you can create any type of gate, perhaps author was confused with 7 colors of white lights, but digital binary world is a way different than the Analog business.
Thanks,
Mansoor Alam
Cancel
Thanks, man. I just needed some clearing up on OR and XOR for some code I'm working on!
Cancel
I am in Middle school and my dad is teaching CS50, a Harvard coding class at a high school, I saw him go over different gates so I build each one in the game Minecraft using Redstone, basically wires.
Cancel
Much better. Thanks!
Cancel
you saved my day thanks guys....

Cancel
If you use a  ~  it will invert your BIT like a NOT gate. example IN ~BI01 will be inverted
Cancel

-ADS BY GOOGLE

File Extensions and File Formats

Powered by:

SearchCompliance

SearchSecurity

  • copyright

    Copyright is a legal term describing ownership of control of the rights to the use and distribution of certain works of creative ...

  • keylogger (keystroke logger or system monitor)

    A keylogger, sometimes called a keystroke logger or system monitor, is a type of surveillance technology used to monitor and ...

  • password

    A password is an unspaced sequence of characters used to determine that a computer user requesting access to a computer system is...

SearchHealthIT

SearchDisasterRecovery

  • business continuity plan (BCP)

    A business continuity plan (BCP) is a document that consists of the critical information an organization needs to continue ...

  • call tree

    A call tree -- sometimes referred to as a phone tree -- is a telecommunications chain for notifying specific individuals of an ...

  • mass notification system (MNS)

    A mass notification system is a platform that sends one-way messages to inform employees and the public of an emergency.

SearchStorage

  • RAID (redundant array of independent disks)

    RAID (redundant array of independent disks) is a way of storing the same data in different places on multiple hard disks to ...

  • data migration

    Data migration is the process of transferring data between data storage systems, data formats or computer systems.

  • compact disc (CD)

    A compact disc is a portable storage medium that can be used for recording, storing and playing back audio, video and other data ...

SearchSolidStateStorage

  • NVMe (non-volatile memory express)

    NVMe (non-volatile memory express) is a host controller interface and storage protocol to enable a solid-state drive to use the ...

  • SSD RAID (solid-state drive RAID)

    SSD RAID (solid-state drive RAID) is a methodology commonly used to protect data by distributing redundant data blocks across ...

  • Tier 0

    Tier 0 (tier zero) is a level of data storage that is faster, and perhaps more expensive, than any other level in the storage ...

SearchCloudStorage

  • RESTful API

    A RESTful application program interface breaks down a transaction to create a series of small modules, each of which addresses an...

  • cloud storage infrastructure

    Cloud storage infrastructure is the hardware and software framework that supports the computing requirements of a private or ...

  • Zadara VPSA and ZIOS

    Zadara Storage provides block, file or object storage with varying levels of compute and capacity through its ZIOS and VPSA ...

Close