It starts with a switch
At the bottom of everything sits the transistor: a microscopic electronic switch that is either on (current flows) or off (it doesn't). A modern CPU contains tens of billions of them, switching billions of times per second. There is no "half on" that the chip can rely on — electrical noise, heat and manufacturing variation make in-between states untrustworthy. Two states, cleanly separated, is the only scheme that works at that scale. And two states is exactly what binary describes: 1 for on, 0 for off.
Logic gates: thinking with switches
Transistors are wired into logic gates — tiny circuits that take one or two bits in and produce one bit out, following simple rules:
| Gate | Rule | Example |
|---|---|---|
| NOT | flips the bit | NOT 1 = 0 |
| AND | 1 only if both inputs are 1 | 1 AND 0 = 0 |
| OR | 1 if either input is 1 | 1 OR 0 = 1 |
| XOR | 1 if the inputs differ | 1 XOR 1 = 0 |
These look trivial, but they're universal building blocks. An XOR gate plus an AND gate makes a half-adder — a circuit that adds two bits. Chain half-adders together and you can add 8-bit, 32-bit or 64-bit numbers. Add some more gates and you get subtraction, comparison ("is A bigger than B?"), and memory cells that hold a bit. Every capability of a computer — arithmetic, decisions, storage — is some arrangement of these gates.
Machine code: the CPU's native tongue
A CPU doesn't understand Python or JavaScript. It understands machine code: fixed patterns of bits where each pattern is one instruction — "add these two registers", "load this memory address", "jump to that instruction". A 32-bit instruction might look like 00000001001010100100000000100000, with different bit fields encoding the operation and its operands. Programmers once wrote these by hand; today, compilers do it. But at the moment of execution, it's always bits.
The CPU runs a relentless loop: fetch the next instruction from memory, decode what its bits mean, execute it — billions of times per second. Everything you see on screen is the accumulated side effect of that loop.
Memory is just bits that stay put
RAM and SSDs are vast arrays of components that each hold one bit — a microscopic capacitor that's charged or not, or a flash cell trapping electrons or not. Your photo isn't "a photo" to the hardware; it's a few million bytes, each byte eight bits, each bit one physical thing in one of two states. File formats (JPEG, MP3, PDF) are simply agreed-upon interpretations of those bit patterns — which is why the same bits can be an image in one program and garbage in another.
The layers above
Nobody thinks in raw bits day to day, because software is built in layers, each hiding the one below:
- Machine code — binary instructions the CPU runs.
- Assembly — human-readable nicknames for machine instructions (
ADD R1, R2). - Compiled languages (C, Rust, Go) — translated to machine code once, then run fast.
- Interpreted languages (Python, JavaScript) — translated line by line as they run.
Each layer trades a little performance for a lot of human sanity. But peel them all away and you're back at transistors switching between 0 and 1 — which is why understanding binary isn't trivia. It's the foundation the whole stack stands on.
Try it yourself
Convert text to binary and see exactly what the machine sees — every character as 8 bits.
Key takeaways
- Transistors are two-state switches — on or off — which is why hardware speaks binary.
- Logic gates (NOT, AND, OR, XOR) combine bits; wired together they add, compare and remember.
- Machine code is raw binary instructions; the CPU fetches, decodes and executes them billions of times per second.
- Memory and storage are just enormous arrays of one-bit holders.
- Programming languages are layers of translation that end, always, in binary.
Frequently asked questions
What is a transistor and why does it matter?
A transistor is a microscopic electronic switch that is either on or off. Billions of them in a CPU switch billions of times per second, and every computation is built from those two-state switches.
What is machine code?
Machine code is the raw binary instruction set a CPU executes directly — patterns of bits that mean add, move, compare or jump. All software is ultimately translated down to machine code.
What do logic gates do?
Logic gates are tiny circuits built from transistors that combine bits using rules like AND, OR and NOT. Wired together, they can add numbers, compare values and make decisions — the basis of all computation.
If computers only understand binary, how do programs work?
In layers. Humans write high-level languages like Python, which are translated to assembly, then to machine code — binary instructions the CPU runs directly. Each layer hides the complexity below it.