Thursday, March 18, 2010

Babbage's Print Automation Engine

The Computer History Museum currently has a functional version of Charles Babbage's engine on display. It's a fascinating and intricate bit of hardware.

Of course once you get past the elegance of the ripple carry and listen to the docents it's clear that the difference engine was actually a print automation engine.

The full engine is shown below and the purpose of this particular version was to compute logarithms to 30 decimal places. This is done with the large right portion of the device.

But the portion on the left that looks like a desk bolted to the side is the part that does something with the results. That's the print automation engine. In this case the final result is a plaster impression that could then be used to create a printing plate. This printing plate could then be used to produce a book of logarithms that could then be taken with you on a boat or in a factory or elsewhere.

So Babbage's engine was intended not just to compute logarithms, it was also intended to make those computations tangible.

1 comment:

  1. Good point. Although almost never discussed from the printing perspective, the main purpose of the BDE was to remove the drudgery and inaccuracies in manually calculated tables of transcendental functions.

    You heard the one about the guy who manually calculated Pi to around 1000 places? About a century later, an electronic computer found an
    error starting near the 500th place. Bummer!

    UPSIDE: Apart from a few minor bugs, the BDE worked as advertised.

    DOWNSIDE: He didn't read and heed Leibniz, so negative numbers are 10's complement and therefore not just a bit flip away.

    The BDE used lookahead-carry rather than ripple-carry, according to "Indeed, Charles Babbage utilized lookahead carries through the part of the Analytical Engine he called an Anticipating Carriage."

    Apparently, you CAN try this at home :)