# Inside the Babbage Difference Engine

May 4, 2008 12:00:00 AM PDT
On Saturday, May 10, in Mountain View, the public will be able to see for the first time a very unusual computer. It's called the Babbage Difference Engine. It weighs nearly five tons and doesn't use electricity.

"The machine works exactly as Babbage intended. There's not a single logical design flaw in the entire design," says its builder Doron Swade.

And 248 gears of iron, brass and steel. The first digital computer is all mechanical, designed by British mathematician Charles Babbage in 1822, but never built.

Swade says of Babbage, "He's famous for two things: inventing computers, and failing to build them."

So, Swade persuaded the Museum of Science in London to complete Babbage's work, and he became Director of the Babbage Project. The one in Mountain View is only the second in existence. It's called a difference engine, because it doesn't multiply; it only adds. That doesn't mean it's a glorified abacus.

It solves complex polynomial equations like this one:

y = 41 + 4x + 7x^2 + x^3 + 5x^4 + 9x^5 + 2x^6 + 8x^7

And it solves them more precisely than any handheld calculator. Set the initial values, clear the memory, and each cycle of the wheel increments the value of x and the value of y. Then, the solution, appears at the other end.

"That is the first successful transference of intelligence to machine."

How similar is this to a modern microprocessor? Well, the on-switch is the crank. Beneath it, a stack of cams acts like the micro-program that controls the operation of all the other parts. Tall bras stacks of 31 digits, rotating gears, are like registers. They store and change the numbers during the calculations. And all of the results are displayed at the end in 3 ways: One stack of gears is like the on-screen display. It also prints the results on paper, and below that it stamps into soft metal something that a typesetter can use. It's the first automatic typesetting machine.

Now, if something goes wrong, how can you tell which gear is jammed where? Voila! The first logic probe is a crowbar!

Never mind the logic, the ballet of brass and steel is positively mesmerizing. Somewhere, Charles Babbage must be smiling. That occurred to Swade, as well.

"I thought, What would he do? He would nod, he would smile, he would know exactly what we were doing, and just carry on."

After the public unveiling, the Babbage machine will remain on display for one year. Some of events on Saturday require registration.

BABBAGE EXHIBIT LAUNCH AND OPEN HOUSE
Saturday, May 10 2008
12:00 Noon - 5:00 PM