The first general-purpose computer was designed in 1837, and never built.
Charles Babbage's Analytical Engine had a memory, a processor, loops and conditional branching, fed by punched cards. In principle it could compute anything a modern computer can. Ada Lovelace wrote what is often called the first program for it. Nearly two centuries later, nobody has yet built one.
Babbage first tried to build a Difference Engine, a special-purpose calculator for mathematical tables, but fell out with his chief engineer and lost government funding. While working on it he realised a much more general machine was possible. From around 1833 he designed the Analytical Engine, first described in 1837.
Its architecture is startlingly modern. A 'store' would hold 1,000 numbers of 40 decimal digits. A 'mill' would do arithmetic and comparisons, relying on internal routines stored as pegs on rotating barrels, roughly like microcode in a modern processor. Programs and data would enter on punched cards borrowed from the Jacquard loom, and results would come out on a printer, a curve plotter or a bell. Because it supported loops and conditional branching, it would have been what is now called Turing-complete.
In 1843 Ada Lovelace translated an Italian description of the engine into English and added extensive notes, including a method for calculating Bernoulli numbers on the machine. That is widely considered the first complete computer program, and she is often called the first programmer, though some historians dispute the title. Babbage himself had written some two dozen programs for the engine between 1837 and 1840.
Babbage built only a small part before his death in 1871. A committee in 1878 called the design a marvel of mechanical ingenuity but recommended against building it. His son Henry built part of the mill, which in 1910 calculated a faulty list of multiples of pi. In 1991 London's Science Museum built Babbage's Difference Engine No. 2 to period tolerances, and it worked. A project called Plan 28, launched in 2010, aims to build the Analytical Engine, but first has to make sense of his voluminous and sometimes inconsistent drawings.
Source: Wikipedia — Analytical engine · Text summarised from Wikipedia (CC BY-SA 4.0)
