Study guide — what to focus on

This module is curated — the teaching is a top free video series (linked in the card above); our job is to point you at the right things, make you understand them, and certify you.

The plan

1. Watch the series (the card above). Ben Eater builds a real 8-bit computer from logic chips, so you see every idea as a working circuit. You don't need to build the hardware — aim to understand the concepts below.
2. Focus on these — they're what the check tests and what everything else in computing is built on:
   • The CPU datapath — the registers (fast on-chip storage), the ALU (does the arithmetic/logic), and the control unit (decodes instructions and tells everything else what to do).
   • The buses — the shared address bus (which location), data bus (the value), and control bus (read/write and timing signals) that connect the CPU to memory and I/O.
   • Memory — RAM holding your program and data; and the memory hierarchy (registers → cache → main memory), where cache hides the speed gap between a fast CPU and slower RAM.
   • The clock — the steady pulse that paces and synchronises every step.
   • The fetch-decode-execute cycle — how the program counter walks through memory and the CPU fetches, decodes, and runs each instruction, forever.
   • Instruction sets & opcodes — the basic operations a CPU understands, and von Neumann vs. Harvard (shared vs. separate instruction/data memory).
3. Explore a CPU hands-on (next section) — step a tiny program through a free online simulator and watch the registers and memory change.
4. Take the K-Check to earn your certificate.

Why this matters

This is the layer underneath every microcontroller, sensor, and board you'll ever design with. When Forge picks an ESP32 or an Arduino for a build, this is what's actually inside it — a datapath fetching instructions from memory over a bus, one clock tick at a time. Understanding the fetch-decode-execute cycle, what registers and buses are, and why cache and clock speed matter gives you the mental model to read a datasheet, reason about why a chip is fast or slow, choose the right microcontroller for a job, and — later — write firmware that fits the machine it runs on.

The ideas stick best when you can watch a CPU run, and you can do that free in your browser with nothing to install. Open the Simple 8-bit Assembler Simulator, a free online model of a tiny CPU: it shows the registers (A, B, C, D and the instruction pointer), a grid of memory, and a small assembly program you can assemble and then step through one instruction at a time. Watching it run is watching the fetch-decode-execute cycle in slow motion.

For a first exploration, load the default program, assemble it, and then click Step instead of Run. On each step, notice the instruction pointer (the program counter) advance, watch which register a value lands in, and see the corresponding memory cell light up as it's read or written. Then try editing a line — change a MOV or add an arithmetic instruction — reassemble, and step through again to confirm it does what you expected. That loop — an instruction is fetched, decoded, and executed, and the machine's state changes — is exactly what Ben Eater's breadboard computer does in hardware, just shown as numbers instead of blinking LEDs.