Binary Logic and Fundamental Gates

In this lesson, you will learn how basic logic gates act as the "decisions" that power every computer by processing binary inputs.

What is a Logic Gate?

At its simplest level, a logic gate is an electronic component that takes one or more binary inputs (0 or 1) and produces a single output based on a fixed rule. You can think of a 0 as "Off" (or Low voltage) and a 1 as "On" (or High voltage).

The Fundamental Gates

The behavior of these gates is best visualized through a Truth Table, which maps every possible input combination to an output.

• NOT: Inverts the signal. If input is 0, output is 1.
• AND: Outputs 1 only if both inputs are 1.
• OR: Outputs 1 if at least one input is 1.

Input A	Input B	AND Output	OR Output
0	0	0	0
0	1	0	1
1	0	0	1
1	1	1	1

Universal and Exclusive Gates

Some gates are combinations of the basics, serving specific architectural needs:

• NAND & NOR: These are "Not-AND" and "Not-OR." They act exactly like their counterparts, but their output is flipped (e.g., NAND outputs 0 only when both inputs are 1).
• XOR (Exclusive OR): Outputs 1 only if the inputs are different. If both are 0 or both are 1, it outputs 0.
• XNOR: The exact inverse of XOR; it outputs 1 only if the inputs are the same.

Visualizing Logic

In computer architecture, we represent these as simple mathematical functions. If we let A and B be our inputs, the XOR gate logic looks like this:

If (A != B) Output = 1
Else        Output = 0

By chaining these gates together, we can perform complex tasks like adding numbers or storing memory. Every processor instruction, from loading data to jumping through code, is ultimately just a result of these gates reacting to bits.

Key Takeaway: Logic gates are the building blocks of computing, using binary rules to transform input states into meaningful output decisions.