How a computer
actually works.

Not a simulation of a lesson about computers — a computer. Sixteen registers, four flags, twenty-seven instructions, and no if statement, so the student builds one. Every exercise starts incomplete: the machine runs, does something, and the class can see exactly what is missing.

Open the exercises Teacher's sheet

exercise 6 · call a subroutine

        CALL seven
        ; ... and now? R3 must hold 9
        HLT
seven:  LDI 7
        MOV R4, R0
        ; how do you get back?

if you never come back, R3 stays 0 — and the machine will tell you.

The nine

About 50–70 minutes for a first lesson, and every one of them is checked by the machine, not by the teacher.

Put a number somewhere

LDI fills the accumulator, MOV moves it

Add two numbers

what ADD Ra, Rb really means

Double a number

SHL is multiply-by-two

Count to ten

a loop needs a counter and a branch

Remember something

STORE and LOAD reach RAM

Call a subroutine

CALL pushes, RET pops — and the code after proves it

Decide something

CMP sets the flags, JZ branches — this is your first if

Say something out loud

OUT hands a byte to a port

What makes it teachable

The starter is wrong on purpose. Running it is not a failure, it is the question — and the check says which register held the wrong value and what was expected.
No partial credit. The machine has no partial answers, so the tick means the program is right, not that it looks right.
Offline, one file, no accounts. A classroom with no internet and a decade-old laptop can run the whole lesson.
Built on the Loom. The machine is weft8.js from app-jacquard, byte for byte — so a student who finishes these eight can open Jacquard or the puzzle set and it is the same computer.

the weft-8 family — one machine, seven faces

the Loomthe machine and its editor — where it all starts Weft Puzzlesfive puzzles solved in assembly, a robot on a grid Clip Loomclipboard programs you can read: strip, squeeze, wrap Weft-8 on hardwarethe same machine in C, three-way parity with the JS one weft8-kitrules small enough to sign off

Weft-8 Classroomyou are here

Weft-8 beside x86 and ARMthe same four jobs in three machines

Every one of these runs the same engine — weft8.js from the Loom, byte for byte. Learn it once and you have learned all seven.

How a computeractually works.