Monday, October 13, 2014

CARDIAC: The Cardboard Computer

I am just so excited about this.

CARDIAC. The Cardboard Computer. How cool is that? This piece of history is amazing and better than that: it is extremely accessible. This fantastic design was built in 1969 by David Hagelbarger at Bell Labs to explain what computers were to those who would otherwise have no exposure to them. Miraculously, the CARDIAC (CARDboard Interactive Aid to Computation) was able to actually function as a slow and rudimentary computer. 

One of the most fascinating aspects of this gem is that at the time of its publication the scope it was able to demonstrate was actually useful in explaining what a computer was. Could you imagine trying to explain computers today with anything close to the CARDIAC?

It had 100 memory locations and only ten instructions. The memory held signed 3-digit numbers (-999 through 999) and instructions could be encoded such that the first digit was the instruction and the second two digits were the address of memory to operate on. The only register was an accumulator.

The simple instruction set would have made for a very easy understanding of how complex programs are able to be built out of simpler sets of operations and data.

Opcode Mnemonic Operation
0INPRead a card into memory
1CLAClear accumulator and add from memory (load)
2ADDAdd from memory to accumulator
3TACTest accumulator and jump if negative
4SFTShift accumulator
5OUTWrite memory location to output card
6STOStore accumulator to memory
7SUBSubtract memory from accumulator
8JMPJump and save PC
9HRSHalt and reset

There is a much longer write up that anyone interested in the beginnings of computers should take a read over. I am hoping to make up my own DIY CARDIAC and try writing some fun programs and if I do I'm going to be sure to post about it.

1 comment:

Kevin Veroneau said...

Hey, great article and thank for you the inspiration. After reading the article, I took it into my own hands to write my own simulator for the Cardiac in Python. I have past experience with bytecode engines in Python, so this project was more or less for readers of my own blog, as I formulated a nice introduction tutorial to how one can build a basic CPU simulator in Python. I hope you can link to it, Building a CPU simulator in Python, this article will also appear shortly on Planet Python.

I write here about programming, how to program better, things I think are neat and are related to programming. I might write other things at my personal website.

I am happily employed by the excellent Caktus Group, located in beautiful and friendly Carrboro, NC, where I work with Python, Django, and Javascript.

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