WDR paper computer
The WDR paper computer or Know-how Computer is an educational model of a computer consisting only of a pen, a sheet of paper, and individual matches in the most simple case. This allows anyone interested to learn how to program without having an electronic computer at their disposal.
The paper computer was created in the early 1980s when computer access was not yet widespread in Germany, to allow people to familiarize themselves with basic computer operation and assembly-like programming languages. It was distributed in over 400,000 copies and at its time belonged to the computers with the widest circulation.
The Know-how Computer was developed by Wolfgang Back and Ulrich Rohde and was first presented in the television program WDR Computerclub in 1983. It was also published in German computer magazines mc and PC Magazin.
The original printed version of the paper computer has up to 21 lines of code on the left and eight registers on the right, which are represented as boxes that contain as many matches as the value in the corresponding register. A pen is used to indicate the line of code which is about to be executed. The user steps through the program, adding and subtracting matches from the appropriate registers and following program flow until the stop instruction is encountered.
The instruction set of five commands is small but Turing complete and therefore enough to represent all mathematical functions: incrementing ("inc") or decrementing ("dec") a register, unconditional jump ("jmp"), conditional jump ("isz", skips next instruction if a register is zero), and stopping program execution ("stp").
The paper computer's method of operation is nominally based on a register machine by Elmar Cohors-Fresenborg, but follows more the approach of John Cedric Shepherdson and Howard E. Sturgis in their Shepherdson–Sturgis register machine model.
- "Ein Meilenstein: der Knowhow-Computer" [A milestone: The Know-how Computer]. WDR Computerclub (in German). Westdeutscher Rundfunk (WDR). 2001-02-08. Archived from the original on 2001-03-31.  
- Rohde, Ulrich (1983). "Computer für Anfänger" [Computer for beginners]. mc (in German). No. 5. Munich, Germany: Franzis Verlag. ISSN 0720-4442.
- Back, Wolfgang (2003). "Der Know-how Computer - Ein Computer, der mit Streichhölzern arbeitet" [The Know-how Computer - A computer working with matches] (in German). Archived from the original on 2019-04-05. Retrieved 2019-04-05. 
- "Papiercomputer – Marian Aldenhövel".
- Cohors-Fresenborg, Elmar (1977). Mathematik mit Kalkülen und Maschinen [Mathematics with calculī and machines] (in German). Vieweg-Verlag. ISBN 3-528-08381-6.
- Shepherdson, John Cedric; Sturgis, Howard E. (April 1963) [December 1961]. "Computability of Recursive Functions". Journal of the ACM. 10 (2): 217–255. doi:10.1145/321160.321170. S2CID 17328540. Retrieved 2019-04-06.
- "Know-How Computer". EduNet Namibia. 2013. Archived from the original on 2014-05-23. 
- Kröger, Chris (2016). "Know How Computer". kroegerama (in German). Archived from the original on 2019-04-05. Retrieved 2019-04-05.