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Hardware/Logic_Gates/Logic_gates.md
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# Logic gates
> [A logic gate consists in] three connections where there may or may not be some electricity. Two of those connections are places where electricity may be put into the device, and the third connection is a place where electricity may come out of the device. (Scott, 2009 p.21)
Logic gates are the basic building blocks of digital computing. **A logic gate is an electrical circuit that has one or more than one input and only one output.** The input controls the output and the logic is isomorphic with [Boolean connectives](../../Logic/Truth-functional_connectives.md) defined in terms of [truth-tables](../../Logic/Truth-tables.md).
Logic gates are the basic building blocks of digital computing. **A logic gate is an electrical circuit that has one or more than one input and only one output.** The input controls the output and the logic determining which types of input (on/off) lead to specific outputs (on/off) is identical to the truth-conditions of the [Boolean connectives](../../Logic/Truth-functional_connectives.md) specifiable in terms of [truth-tables](../../Logic/Truth-tables.md).
> [A gate consists in] three connections where there may or may not be some electricity. Two of those connections are places where electricity may be put into the device, and the third connection is a place where electricity may come out of the device. (Scott, 2009)
Physically, what 'travels through' the gates is electrical current and what constitutes the 'gate' is a transistor responding to the current. But on a more abstract level it is bits that go into the gate and bits which come out: binary information that may be either 1 or 0.
## References

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Hardware/Logic_Gates/Nand_gate.md
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In practice, it is more efficient to use specific dedicated gates (i.e OR, AND, NOT etc) for the other Boolean connectives but in principle the same output can be achieved through NANDs alone.
## More complex outputs from combining NANDS
The example we have looked at so far is fairly simple because there is just one NAND gate corresponding to two inputs (the two switches) and one output (the bulb). These specific gates are detailed in the next section.
When we add more NAND gates and combine them with each other in different ways we can create more complex output sequences and these too will have corresponding truth tables.