Der Know How Computer

The Know How paper computer, also called the WDR papiercomputer is a "paper computer" that is meant to be a simulation of a computer using paper, a very small instruction set, and your head to compute it. It was invented by Wolfgang Back and Ulrich Rohde. It was introduced in West German TV and in MC magazine in 1983. It is effectively a notation for counter machines.

It has four registers, labeled 1 through 4, and five instructions. Here are the list of instructions:

1. + [register]: Adds 1 to the register.
2. - [register]: Subtracts 1 to the register.
3. J [line]: Jumps to the given line number.
4. 0 [register]: Checks if the given register is zero. If not zero, it continues like normal. If zero, skips one line ahead of it.
5. Stop: Halts program.
   

Below are some examples of code:

Cleaning the 1 register:

0 1
J 4
STOP
- 1
J 1

Adding the first and second registers, and outputting them in the first register:

0 2
J 4
Stop
- 2
+ 1
J 1

Multiplication:

0 2
J 4
J 8
- 2
+ 4
+ 1
J 1
0 4
J 11
J 14
- 4
+ 2
J 8
- 3
0 3
J 1
0 2
J 20
STOP
- 2
J 17