These plans depict a machine with a mill (the CPU, capable of doing addition, subtraction, multiplication and division), a store (the memory), and the barrels (microcode for the mill operations). It's the closest thing to a computer as we know it (although the program and the data are stored separately and programs have no way of accessing anything other than fixed memory locations: i.e. there are no references or pointers).
If you are following along and want some reading then go with the following:
- The Difference Engine by Doron Swade. It's an easy, quick read introduction to Babbage, the Engines and the reconstruction of Difference Engine No. 2. The latter reconstruction demonstrates that the construction techniques available to Babbage were sufficient and would have enabled the construction of the machine. The reconstruction cost £250,000 in the late 1980s.
- The Little Engines that Could've. This is a PhD thesis by Bruce Collier and goes into a lot of detail about the operation of Babbage's engine. I turned those web pages into PDF and had it bound so I could sit and read it. The PDF is here.
- Charles Babbage's Analytical Engine, 1838. IEEE article by the man who probably understood Babbage's Engines better than anyone in the 20th century, Allan Bromley. This article introduces the state of the machine as of 1838.
- Babbage's Analytical Engine Plans 28 and 28a-The Programmer's Interface. Also by Allan Bromley this paper covers the Analytical Engine in 1847 when Babbage stopped working on it. In particular, it details the instruction set that would have been available to the programmer.
- The Evolution of Babbage's Calculating Engines. More historical context from Allan Bromley putting the design of the Analytical Engine in context with the Difference Engines and modern computers.
- Babbage's Analytical Engine Babbage's son, Major-General H. P. Babbage, describes his construction of part of the Analytical Engine.
- The Analytical Engine Also by Babbage's son, this long paper describes the operation of the Analytical Engine as he understood it.
- Of The Analytical Engine Charles Babbage's own description of the Analytical Engine from his autobiography.
- Sketch of the Analytical Engine The famous paper translated by Ada Lovelace on which much of her fame rests.
And as a bonus, here are some pictures I took at the weekend in the Science Museum in London.
The first shows a trial portion of the Difference Engine:
Here are some punched cards prepared by Babbage that would have been used for programming the Analytical Engine:
And here's the trial section of the Analytical Engine that Babbage built:
And, finally, the mill of the Analyical Engine. This was built by Babbage's son after his father's death.