<computer, history> Charles Babbage's design for the first automatic
mechanical calculator. The Difference Engine was a special purpose device
intended for the production of mathematical tables. Babbage started work on the
Difference Engine in 1823 with funding from the British Government. Only
one-seventh of the complete engine, about 2000 parts, was built in 1832 by
Babbage's engineer, Joseph Clement. This was demonstrated successfully by
Babbage and still works perfectly. The engine was never completed and most of
the 12,000 parts manufactured were later melted for scrap.
It was left to Georg and Edvard Schuetz to construct the first working devices
to the same design which were successful in limited applications. The Difference
Engine No. 2 was finally completed in 1991 at the Science Museum, London, UK and
is on display there.
The engine used gears to compute cumulative sums in a series of registers: r[i]
:= r[i] + r[i+1]. However, the addition had the side effect of zeroing r[i+1].
Babbage overcame this by simultaneously copying r[i+1] to a temporary register
during the addition and then copying it back to r[i+1] at the end of each cycle
(each turn of a handle).
Difference Engine at the Science Museum.
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