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.
|0||INP||Read a card into memory|
|1||CLA||Clear accumulator and add from memory (load)|
|2||ADD||Add from memory to accumulator|
|3||TAC||Test accumulator and jump if negative|
|5||OUT||Write memory location to output card|
|6||STO||Store accumulator to memory|
|7||SUB||Subtract memory from accumulator|
|8||JMP||Jump and save PC|
|9||HRS||Halt 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.