The programming architecture of Babbage's Analytical Engine

Prof. Dr. Raul Rojas

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The mathematician and inventor Charles Babbage wrote 26 programs between 1836 and 1841 for the unfinished "Analytical Engine" (AE). The code is embedded implicitly in tables summarizing program traces. In this talk, I present the programming architecture of Babbage’s mechanical computer based on the first code written for the machine. The AE had a processor separate from memory, and worked using a kind of dataflow approach. The stream of arithmetical operations was independent from the stream of memory addresses. Special "combinatorial" cards allowed the processor to execute FOR and WHILE loops. Combinatorial cards also allowed independent looping through the stream of memory addresses. Quite sophisticated computations were possible and illustrate why Babbage talked about the possibility of doing "algebra" with his machine. The programs I will discuss predate by several years the account published by Menabrea in 1842 and translated later by Lady Lovelace with notes of her own.