Computer history museum


I took a day of vacation yesterday, and Jacky, Friedrich, Petra and I went to the Computer History Museum in Mountain View, where we spent many hours being impressed.


One of the most impressive things is the 2000 year old Antikythera astronomical computer, gears and wheels and amazingly well constructed, considering the technology of the time. There is no actual device here — the actual device is in the national archaeological museum in Athens —  just videos (which are also on the web site) and the picture above, but it’s still fascinating. I imagine 99.9% of visitors walk past without noticing it.


There is far too much to see, and I took far too many pictures, to include them all — besides, it would be redundant with the museum’s own site. Some of the machines look like abstract art.



A Google street-view bicycle. I think there is an ambition to have street views of bicycle trails, maybe even mountain bike trails, but not with this size and weight.

Of course, the highlight of the entire museum is the Babbage difference engine, and its live demo.


Babbage wanted to compute mathematical tables. The difference engine is good for computing sequential values, but only sequential values. Okay for tables, but not a general purpose computing engine.

His collaborator, Ada lady Lovelace, was arguably aware of the more general purposes that could be served by a more general machine. It was not clear from the docent demo whether the Babbage analytical engine, which has never been built, could have been used as a general purpose computer or not.

We are told that the drawings for the analytical engine are under study to see whether it would be feasible to build one. Unfortunately, the design is incomplete, so gaps need to be filled in, by a committee of antiquarian expert engineers who ask, “What would Babbage have done?”


I have read that electromagnetic relays had been developed by 1830 to the point that Babbage actually could have designed an electrical computer, had he been more into electrical devices than mechanical. History might have been quite different if the electronic computer had been implied by the existence of electrical computers 150 years earlier than actually happened.

Babbage’s interest in computing mathematical tables began when he noticed that the tables of his day were full of errors. Even in the early 19th century, errors in the numbers could cause disasters in buildings, bridges, machines. Many of the errors were in transcription of the results, so this difference engine includes a printer that could impress one line at a time into soft plaster. The finished page could then be used to cast type for printing.


The printer is at the opposite end of the machine from the poor sod turning the crank, so there is a linkage from the printer that stops the machine when the page is full and needs a new tray of soft plaster.

And speaking of poor sods, the original Babbage design envisioned P. Sod turning the crank once per machine cycle, but did not understand how much force would be required. The committee of experts added a 4:1 reduction gear to the hand crank, meaning that P. Sod turns the crank four times per machine cycle. This is an example of the kind of thing that Babbage would very likely have done had he built the machine himself.



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