Mechanical computer
January 23, 2012
In 1837, the famed English engineer, Charles Babbage, drew up plans for a mechanical computer. Made of brass and iron and powered by steam, the Analytical Engine was designed 100 years before mathematician Alan Turing laid out the principles of modern computing that paved the way for modern, electronic computers.
Babbage’s machine is recognizable as a general purpose computer - but it was never built, and knowledge of its design remained largely unknown to 20th century engineers.
This year, however, Doron Swade, a computer historian, and programmer John Graham-Cumming are working to build the Analytical Engine, nearly two centuries after it was first designed.
"The Analytical Engine incorporates almost every logical feature of a modern digital electronic computer," Swade told Deutsche Welle, "except it's mechanical, so it is in a sense the 'Ur' machine of computing."
Known as Plan 28, the project will be officially launched in the coming weeks. The duo already have about 120,000 euros ($154,000) in pledges. They estimate the entire project will cost about 12 million euros ($15.4 million), mainly to come from private donations.
None of the drawings for the Analytical Engine is complete. So Swade and Grahame-Cumming's first job is to make a complete set of drawings using Babbage’s notebooks, which have been digitized by London’s Science Museum.
Ingenious design
After that, Graham-Cumming and Swade will generate a three-dimensional virtual model and construction will begin. They hope to have the engine up and running in about 10 years.
Graham-Cumming, Plan 28’s executive director, said a mechanical computer works almost exactly like an electronic one.
"It had memory, although made of brass rather than silicon. It had a central processing unit, the chip, the central part of the machine, made of cogs," he told Deutsche Welle. "It had a program on cards made of paper pasted together or ivory, and it even had a printer."
Graham-Cumming added that the engine would have had about a kilobyte of memory – about a million times less than today’s average laptop.
He described the memory as stacks of brass cogs, each one containing the numbers 0 through 9. With a stack of them, you could write a number up to about 30 digits long.
Familiar programming
The Analytical Engine's central processing unit, which Babbage called the mill, was even more complicated. In addition to simple mathematical procedures, it had to perform the so-called comparison operation. That is the ability to look at the computer's own memory, read the numbers, and then make a decision.
According to Graham-Cumming, anyone who has done basic computer programming today would very quickly be able to work out how to program the analytical engine. Using basic arithmetic, you could use the memory to represent different things.
One of the main motivations for the project is to consider how the history of information technology might have changed if Babbage had actually built his Engine.
Missed opportunity?
"Could you have had an information age in the 19th century had Babbage succeeded?" Swade said. "Could you have built these things out of machinery? Or did the world have to wait for the children of the silicon age to implement the principles of computing, because the principles were embodied in his designs?"
Swade rejects the notion that Babbage never built his machines due to the limitations of 19th century engineering.
Swade previously led a 17-year-long project to build another of Babbage's Engines, called Difference Engine Number Two. The five-ton mechanical calculator is made of 8,000 parts, which the Briton has gotten working.
When the 20th century pioneers of modern computing began their work, they reinvented Babbage's principles largely in ignorance of his work. However, in the next few years, Plan 28 should be able to show us just how close their precursor came.
Author: Molly Guinness, London / srs
Editor: Cyrus Farivar