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Computer Internals
NewNew: watch every micro-operation on the system bus

How a computer really works, layer by layer.

Follow a single line of C down through assembly, machine code, micro-operations and buses to the logic gates and transistors that run it — and step through every one of them live.

Open the simulatorExplore the levels
levels of abstraction
7
levels of abstraction
chapters planned
41
chapters planned
runnable examples
24
runnable examples
installs or sign-ups
0
installs or sign-ups

The simulator

Stop imagining what the CPU does. Watch it.

A compiler, an emulator and a debugger that explain themselves — running entirely in your browser.

int c = a + b;→mov eax, DWORD PTR [rbp-4]mov ecx, DWORD PTR [rbp-8]add eax, ecxmov DWORD PTR [rbp-12], eax
if (c > 7)→cmp DWORD PTR [rbp-12], 7jle .L1

C → assembly, in your browser

A real compiler with types, pointers, structs and strings. Every assembly line maps back to the C that produced it.

OF0
SF1
ZF0
AF1
PF0
CF1

cmp eax, 5 · 3 − 5 = −2 → jl taken

Every flag, every bit

The full RFLAGS register, what each instruction wrote or changed, and which conditional jump will be taken — and why.

▸ factorial(n=3) · ← factorial(n=4) ← main()
[rbp-4]argn0x00000003
[rbp]fpsaved rbp (factorial)0x7fffff98
[rbp+8]retreturn → factorial+140x00401011

The stack, labeled

Frames, locals, arguments, saved frame pointers and return addresses, named from your C source. Watch a buffer overflow smash one.

CPUMAR · MDR
Address0x7fffffc8
Data0x7fffffe0 →
ControlMEMW
RAMstack

Inside the CPU

Fetch, decode, address calculation, bus reads and writes, ALU, write-back — each micro-operation animated on the system bus.

Seven levels

One line of code, seven levels deep

Every level is implemented by the one below it. Pick any level to zoom in.

Explore the levels
  1. L0Programming languagesWhat you write: variables, functions, pointers — and what a compiler turns them into.
  2. L1Assembly languageOne line per instruction: registers, flags, jumps — the view debuggers and disassemblers give you.
  3. L2Operating systemThe layer that turns one CPU into many processes: virtual memory, system calls, files.
  4. L3Instruction set architectureThe contract between software and silicon: instruction formats, encodings, addressing modes.
  5. L4MicroarchitectureHow one instruction becomes fetch, decode, execute: datapath, buses, caches and pipelines.
  6. L5Digital logicGates, adders, the ALU, flip-flops and memory cells — where 0 and 1 become arithmetic.
  7. L6Devices & physicsThe bottom of the stack: transistors as switches, CMOS gates, and how chips are made.

Foundations

The number systems every level relies on.

Binary and hexadecimalTwo’s complement and signed numbersFloating point (IEEE 754)Characters, ASCII and UnicodeEndianness

Start at the top. Go as deep as you like.

No install, no account. Pick an example and press Step.

Open the simulator