Logic Gate
A physical device implementing a basic Boolean operation, the hardware atom of digital computation.
Definition
A logic gate is an electronic circuit that computes one Boolean function of its inputs. The basic gates are AND, OR, and NOT; derived gates include NAND, NOR, XOR, and XNOR.
Real gates have finite switching speed and consume power on each transition, so a circuit's timing and energy use, not just its logic, constrain design. Propagation delay through chains of gates ultimately caps how fast a synchronous system can be clocked.
The dominant fabrication technology, complementary metal-oxide-semiconductor logic, builds every gate from pairs of transistors arranged to draw significant power only while switching. This is why a chip's power and heat scale with how often its gates toggle, and why clock speed, power, and cooling are linked constraints. Understanding the gate as a physical, power-consuming device, not just a logical symbol, is essential to real design.
Functional completeness
NAND alone (or NOR alone) is functionally complete: any Boolean function can be built from NAND gates. This is why fabrication processes can standardize on one gate type and still realize arbitrary logic.
| A | B | A NAND B |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
Why it matters
Gates are the physical realization of Boolean algebra. Combining them builds adders, multiplexers, memory, and ultimately processors. Gate count and switching delay set a circuit's size and speed.
Fusion connection
Fast gate-level logic in field-programmable devices handles the microsecond-scale interlocks and signal routing in fusion plant control and diagnostics.