Booting Up a Computer Pioneer’s 200-Year-Old Design

Charles Babbage, the grandfather of the computer, envisioned a calculating machine that was never built, until now

  • By Aleta George
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Charles Babbage
Frustrated by human error, mathematician and inventor Charles Babbage designed a machine to perform mathematical functions and automatically print the results. (Library of Congress)

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Charles Babbage differential calculating machine

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Charles Babbages Difference Machine No. 2

Charles Babbage's Difference Machine No. 2


When today’s number crunchers want to make quick calculations, they reach for their smartphone, a device practically unimaginable two centuries ago. But in the 1820s, at least one forward-thinking mathematician envisioned a calculating machine, albeit far from portable. Frustrated by the human errors he found in printed numerical tables, English inventor Charles Babbage designed a machine to perform mathematical functions and automatically print the results. His initial design, which called for 25,000 parts, would have weighed 15 tons and been about the size of a horse-drawn carriage.

The plans looked good on paper, but Babbage was never able to build his machine. More than a century after his death in 1871, computer historians blew the dust off his 5,000 pages of notes and drawings and wondered if his ideas could work. In 1991, on the bicentennial of Babbage’s birth, the Science Museum in London unveiled his Difference Engine No. 2, a fully functioning calculating machine, built to the specs of the inventor’s drawings. A full-scale clone of that machine is now on display in Mountain View, California, at the Computer History Museum through December 2009.

Babbage called his invention a “difference engine” because its function is based on the mathematical principle of finite differences, which calculates complex mathematical functions by repeated addition without the use of multiplication or division. Constructed in a cast-iron frame, the machine on display is 11 feet long and 7 feet tall. With each turn of its crank, steel and bronze cams and rods spring into precise action, clicking softly like a Victorian clock. Spinning steel brackets and columns of gearwheels, which represent numbers, create a fluid mechanized helical dance. There are no touch screens, of course, but after four cranks, the machine can calculate an algebraic equation in six seconds.

Babbage was born in 1791 at the onset of England’s Industrial Revolution. He studied at Cambridge, and thanks to an inheritance from his wealthy father, had leisure time to think about how things worked and improve on them. Babbage invented the cowcatcher, a device on the front of a train that clears debris without slowing the train. He also improved lighthouse signaling and created a quick-release system for railway carriages. Living amid all the wondrous changes wrought by the industrial age, Babbage, surveying yet another error-ridden set of printed numerical tables, once exclaimed: “I wish to God these calculations had been executed by steam!”

Up until 40 years ago, engineers, navigators, astronomers and bankers used slide rules and books of tables to perform calculations. “The defining event which brought the end of the slide rule and the books of tables was in 1972, when Hewlett-Packard introduced the HP-35,” says the computer museum’s senior docent, Tim Robinson. “This was the first hand-held, full-function scientific calculator that replaced all the normal functions of tables and the slide rule.”

Though the exact creator of the very first calculator is debatable, Babbage is counted among the pioneers who designed a machine that could reliably compute equations. In an attempt to build his difference engine in the 1830s, Babbage secured funding from the British government and commissioned engineer and toolmaker Joseph Clement to make the 25,000 parts. When Clements had finished about half the parts, he and Babbage had an irreconcilable dispute and the project was halted.


When today’s number crunchers want to make quick calculations, they reach for their smartphone, a device practically unimaginable two centuries ago. But in the 1820s, at least one forward-thinking mathematician envisioned a calculating machine, albeit far from portable. Frustrated by the human errors he found in printed numerical tables, English inventor Charles Babbage designed a machine to perform mathematical functions and automatically print the results. His initial design, which called for 25,000 parts, would have weighed 15 tons and been about the size of a horse-drawn carriage.

The plans looked good on paper, but Babbage was never able to build his machine. More than a century after his death in 1871, computer historians blew the dust off his 5,000 pages of notes and drawings and wondered if his ideas could work. In 1991, on the bicentennial of Babbage’s birth, the Science Museum in London unveiled his Difference Engine No. 2, a fully functioning calculating machine, built to the specs of the inventor’s drawings. A full-scale clone of that machine is now on display in Mountain View, California, at the Computer History Museum through December 2009.

Babbage called his invention a “difference engine” because its function is based on the mathematical principle of finite differences, which calculates complex mathematical functions by repeated addition without the use of multiplication or division. Constructed in a cast-iron frame, the machine on display is 11 feet long and 7 feet tall. With each turn of its crank, steel and bronze cams and rods spring into precise action, clicking softly like a Victorian clock. Spinning steel brackets and columns of gearwheels, which represent numbers, create a fluid mechanized helical dance. There are no touch screens, of course, but after four cranks, the machine can calculate an algebraic equation in six seconds.

Babbage was born in 1791 at the onset of England’s Industrial Revolution. He studied at Cambridge, and thanks to an inheritance from his wealthy father, had leisure time to think about how things worked and improve on them. Babbage invented the cowcatcher, a device on the front of a train that clears debris without slowing the train. He also improved lighthouse signaling and created a quick-release system for railway carriages. Living amid all the wondrous changes wrought by the industrial age, Babbage, surveying yet another error-ridden set of printed numerical tables, once exclaimed: “I wish to God these calculations had been executed by steam!”

Up until 40 years ago, engineers, navigators, astronomers and bankers used slide rules and books of tables to perform calculations. “The defining event which brought the end of the slide rule and the books of tables was in 1972, when Hewlett-Packard introduced the HP-35,” says the computer museum’s senior docent, Tim Robinson. “This was the first hand-held, full-function scientific calculator that replaced all the normal functions of tables and the slide rule.”

Though the exact creator of the very first calculator is debatable, Babbage is counted among the pioneers who designed a machine that could reliably compute equations. In an attempt to build his difference engine in the 1830s, Babbage secured funding from the British government and commissioned engineer and toolmaker Joseph Clement to make the 25,000 parts. When Clements had finished about half the parts, he and Babbage had an irreconcilable dispute and the project was halted.

After a decade of work, all Babbage had to show for his efforts was a small demonstration machine, used to impress parlor guests at his Saturday soirees. Both Charles Dickens and Charles Darwin turned the handle of the machine that was considered an engineering breakthrough for its time. Often referred to as the “beautiful fragment,” it is one of the most prized artifacts in the London Science Museum.

Once he lost his financial backers for the calculating machine, Babbage designed and partially built an ambitious device he would call the “Analytical Engine.” Tinkering with it for many years, he applied many of the same principles and features found in today’s computers, including programmable punch cards and iteration. It is mainly because of his Analytical Engine that Babbage is considered the “grandfather of the computer.”

“He was a thoroughly modern thinker in how he thought about computing,” said former Microsoft technology officer Nathan Myhrvold in a lecture at the Computer History Museum.

Using what he had learned developing the Analytical Engine, Babbage modified the design of his difference calculating machine but died before he could build it. Toward the end of the 20th century, several computer geeks pored over his designs. Doron Swade, then the curator of computing at the Science Museum in London, decided to build the Difference Engine No. 2 without knowing for sure if it would work. It took him 17 years, but when he finished, it worked just as Babbage said it would.

The difference engine was nearly ready for Babbage’s birthday celebration, but the project ran out of money before completion of the machine’s typeset and print functions. When Microsoft’s Bill Gates saw the work in progress, he suggested that Myhrvold, who's an inventor, archaeologist and investor, might finance the completion of it. Only if the London Museum agreed to build a working replica for his private collection, Myhrvold said in sealing the deal. After the colossal calculator leaves the Silicon Valley museum, it’s bound for Myhrvold’s home in Seattle, perhaps joining the Tyrannosaurus rex skeleton in his living room.

Meanwhile, the machine is demonstrated Wednesday through Friday at 2 p.m. and on weekends at 1 and 2 p.m. During a recent visit, a docent turned the crank of the foot-wide wheel, putting her back into it. As the gears and cams clicked into motion, one onlooker remarked that the movement looked like the double helix of DNA. The audience seemed mesmerized by the calculator’s elegant precision. At long last, Babbage’s genius was getting its due.


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Comments (9)

i love CB :) Charles Babbage !! LolxD:)

Posted by Zalina Hakens on April 15,2012 | 02:57 PM

Greeting I am now 85 years young, but when my mother, Mildred Lynn Engdahl, worked at an insurance company in Chicago, she was what was called a "punch card" operator. It was a rather back-breaking process and she would come home with somewhat bloody fingers.

I had read several years ago that this machine was the forerunner of the computer. Any comments? Thanks

P.S. It is also history that the weaving loom really was the earliest forerunner of the computer???

Posted by Carol E. Still on April 22,2009 | 09:13 AM

I especially liked how Babbage used his leisure time. I believe we no longer need to be very wealthy to enjoy some leisure time. The difference is what we do with it. Part of being human is to be creative.

Posted by Lilian Dyer on April 13,2009 | 10:36 AM

Babbage's "computer" is a remarkable item. Still I cannot help but wonder how the ancient Greeks achieved so many mathematical discoveries using a number system based on their alphabet and without the need of the touted Arabic zero. They calculated the dimensions of the planet on which we live within 50 miles of the the precise measurements in use with modern technology. They discovered the value for "pi" and demonstrated that it was an infinite number. The recent finding in a long sunken Greek vessel of a "calculator" with intricate gear systems allowing the navigator of the ship to determine the distance traveled and how far they were from their desination is far more impressive to me than the computer that Babbage could not build in the days of the Industrial Revolution. Think about it!

Posted by John P. Nasou, M.D. on April 10,2009 | 09:00 PM

Fascinating read. I wish there were a picture of the machine for those us who are unable to see it in person in Silicon Valley. I hope Myhrvold’s home in Seattle can host visitors! It's so amazing to me to know there are (were) people like Babbage who can think of weighty thoughts out of thin air and proceed to act on them. Great article. D

Posted by Danny Tariku on April 10,2009 | 10:14 AM

The quiet clicking of gears and cams (presumably) reminded me of Ottmar Mergenthazler's Linotype machine which revolutionized typesetting and printing from 'lines of type.' That huge iron, brass and aluminum beast gave way to computerized methods, but reluctantly, as letter images were improved slowly.

Posted by Arthur B. Darwin on April 9,2009 | 07:06 PM

It's a beautiful sight! The exhibit may end soon - the Computer History Museum site doesn't say when. When we visited San Francisco last spring, we made sure to plan an afternoon to see this difference engine and the museum as well. Don't miss it!

Posted by Claudia Lowenstein on April 9,2009 | 02:40 PM

If this is so important, why has the Smithsonian in DC removed the "history of computing" displays from their collection? No difference engine replica, no IBM 360, no Apple I... zip. For a business that's central to America it's a travesty that the museum in DC is silent.

Posted by gary brown on April 9,2009 | 02:35 PM

and what of Ada Lovelace?

Posted by tony williams on April 9,2009 | 02:21 PM

This replica is of a difference engine, which can calculate tables of functions. Babbage went on to design a fully programmable machine with the crucial addition of a conditional branch instruction, where the sequence of actions varies according to a calculated result. This machine used punched cards to store programs and data. Is it not time to explore making a working model of this "analytic engine"?

Posted by Henry Casson on April 6,2009 | 01:36 PM



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