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Diff — Analytical Engine

Comparing rev 2 → rev 3

	The Analytical Engine was [[Charles Babbage]]'s design for a general-purpose programmable computer, worked out through the 1830s–1860s and never completed. Had it been built, it would have been the first Turing-complete machine — a century before Turing.

	## The design

	Where the Difference Engine could only grind out tables, the Analytical Engine was meant to compute anything. Its architecture reads like a modern machine in Victorian brass:

	- The store — memory holding roughly 1,000 numbers of 50 digits each.
	- The mill — the arithmetic unit: today's CPU.
-	- Punched cards — borrowed directly from the [[Jacquard Loom\|Jacquard loom]]: operation cards carried instructions, variable cards carried data.
-	- Conditional branching and loops — the machine could change its course based on results, the feature that makes a calculator into a computer.
-	- A printer and plotter — output cast in type, ready to publish.
+	- [[Punched card\|Punched cards]] — borrowed directly from the [[Jacquard Loom\|Jacquard loom]]: operation cards carried the instruction stream, variable cards carried the data — program and input as separate decks.
+	- Conditional branching and loops — the machine could back the card reader up and repeat a section, or change its course based on a result: the feature that makes a calculator into a computer.
+	- A printer, plotter, and bell — output cast in type ready to publish, and a bell that rang when the engine needed an operator.

-	In modern terms: memory, processor, program, conditionals, I/O. Every computer since — including the one serving this page — follows that plan.
+	In modern terms: memory, processor, program, conditionals, I/O. Every computer since — including the one serving this page — follows that plan. Babbage even designed what we'd now call microcode: each high-level operation decoded into finer mechanical steps. And he understood the machine's most unsettling property — it could surprise its operator with results no one had hand-computed. When asked what would happen if the wrong numbers went in, he gave computing's first debugging quote: "I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question."

	## Lovelace's program

	In 1843 [[Ada Lovelace]] published her translation of Luigi Menabrea's account of the engine, with notes three times longer than the paper itself. Note G contained a worked method for computing [[Bernoulli numbers]] on the machine — widely called the first published computer program. More than the algorithm, she grasped what the cards meant: if numbers could stand for things, the engine could manipulate symbols — it might compose music, process language, work with ideas. Babbage designed a number machine; Lovelace described a general-purpose thinking machine.

	## Never built

-	The engine defeated Victorian machining: tens of thousands of precision parts were beyond any workshop, and after the Difference Engine's collapse no government would fund another Babbage machine. His son Henry demonstrated a fragment of the mill in 1888 — it computed, correctly, a sliver of the design.
+	The engine defeated Victorian machining: tens of thousands of precision parts were beyond any workshop, and after the Difference Engine's collapse no government would fund another Babbage machine. His son Henry Babbage demonstrated a fragment of the mill in 1888 — it computed, correctly, a sliver of the design, printing multiples of π to 29 places.

-	Modern verdicts have settled the question. The 1991 reconstruction of Difference Engine No. 2 proved Babbage's engineering was sound, and the ongoing Plan 28 project continues to study building the Analytical Engine from his surviving plans. It was not a fantasy; it was a machine built too early, waiting for its century.
+	Modern verdicts have settled the question. The 1991 reconstruction of Difference Engine No. 2 proved Babbage's engineering was sound, and the ongoing Plan 28 project continues to study building the Analytical Engine from his surviving plans — some 300 drawings and 2,000 pages of notation. It was not a fantasy; it was a machine built too early, waiting for its century.

	## See also

	- [[Charles Babbage]]
	- [[Ada Lovelace]]
+	- [[Bernoulli numbers]]
+	- [[Punched card]]
	- [[Jacquard Loom]]
	- [[History of Programming]]

	[[Category:History]]
	[[Category:Hardware]]

	The Analytical Engine was [[Charles Babbage]]'s design for a general-purpose programmable computer, worked out through the 1830s–1860s and never completed. Had it been built, it would have been the first Turing-complete machine — a century before Turing.

	## The design

	Where the Difference Engine could only grind out tables, the Analytical Engine was meant to compute anything. Its architecture reads like a modern machine in Victorian brass:

	- The store — memory holding roughly 1,000 numbers of 50 digits each.
	- The mill — the arithmetic unit: today's CPU.
-	- Punched cards — borrowed directly from the [[Jacquard Loom\|Jacquard loom]]: operation cards carried instructions, variable cards carried data.
-	- Conditional branching and loops — the machine could change its course based on results, the feature that makes a calculator into a computer.
-	- A printer and plotter — output cast in type, ready to publish.
+	- [[Punched card\|Punched cards]] — borrowed directly from the [[Jacquard Loom\|Jacquard loom]]: operation cards carried the instruction stream, variable cards carried the data — program and input as separate decks.
+	- Conditional branching and loops — the machine could back the card reader up and repeat a section, or change its course based on a result: the feature that makes a calculator into a computer.
+	- A printer, plotter, and bell — output cast in type ready to publish, and a bell that rang when the engine needed an operator.

-	In modern terms: memory, processor, program, conditionals, I/O. Every computer since — including the one serving this page — follows that plan.
+	In modern terms: memory, processor, program, conditionals, I/O. Every computer since — including the one serving this page — follows that plan. Babbage even designed what we'd now call microcode: each high-level operation decoded into finer mechanical steps. And he understood the machine's most unsettling property — it could surprise its operator with results no one had hand-computed. When asked what would happen if the wrong numbers went in, he gave computing's first debugging quote: "I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question."

	## Lovelace's program

	In 1843 [[Ada Lovelace]] published her translation of Luigi Menabrea's account of the engine, with notes three times longer than the paper itself. Note G contained a worked method for computing [[Bernoulli numbers]] on the machine — widely called the first published computer program. More than the algorithm, she grasped what the cards meant: if numbers could stand for things, the engine could manipulate symbols — it might compose music, process language, work with ideas. Babbage designed a number machine; Lovelace described a general-purpose thinking machine.

	## Never built

-	The engine defeated Victorian machining: tens of thousands of precision parts were beyond any workshop, and after the Difference Engine's collapse no government would fund another Babbage machine. His son Henry demonstrated a fragment of the mill in 1888 — it computed, correctly, a sliver of the design.
+	The engine defeated Victorian machining: tens of thousands of precision parts were beyond any workshop, and after the Difference Engine's collapse no government would fund another Babbage machine. His son Henry Babbage demonstrated a fragment of the mill in 1888 — it computed, correctly, a sliver of the design, printing multiples of π to 29 places.

-	Modern verdicts have settled the question. The 1991 reconstruction of Difference Engine No. 2 proved Babbage's engineering was sound, and the ongoing Plan 28 project continues to study building the Analytical Engine from his surviving plans. It was not a fantasy; it was a machine built too early, waiting for its century.
+	Modern verdicts have settled the question. The 1991 reconstruction of Difference Engine No. 2 proved Babbage's engineering was sound, and the ongoing Plan 28 project continues to study building the Analytical Engine from his surviving plans — some 300 drawings and 2,000 pages of notation. It was not a fantasy; it was a machine built too early, waiting for its century.

	## See also

	- [[Charles Babbage]]
	- [[Ada Lovelace]]
+	- [[Bernoulli numbers]]
+	- [[Punched card]]
	- [[Jacquard Loom]]
	- [[History of Programming]]

	[[Category:History]]
	[[Category:Hardware]]