The Annotated Turing: A Guided Tour Through Alan Turing's Historic Paper on Computability and the Turing Machine [Paperback]

Turing's 1936 Paper "On Computational Numbers" is often cited as a landmark in the history of computing, but it's details are not widely considered or well known today. If you're curious to know more about the Paper, and why it's important, you can do no better than read this book. It contains a complete transcript of the original Paper, with extensive commentary and explanation from Petzold that make the Paper accessible and understandable to a wider audience (and even for specialists, this book is probably a better choice than just reading the original Paper!). Petzold's enthusiasm for the topic shines through in an excellent writing style, striking a good balance between detailed technicalities and simpler descriptions, in a friendly helpful way that will neither confuse the layman nor bore the expert.

Petzold supplies invaluable historical context: some of the developments in mathematics in the late nineteenth and early twentieth centuries that undoubtedly influenced Turing, and which appear explicitly in the paper. This is a very useful aid to understanding Turing's paper for readers not expert in those topics of mathematics (which is almost all of us who don't have post-graduate degrees in very specialised areas of pure maths!). But the book is definitely aimed at readers with some mathematical background and aptitude. If (UK) O-level / GCSE maths was a mystery to you, you may struggle; if you have A-level maths or computing you'll be fine. If you're somewhere in between, Petzold's explanations will happily guide you through the details.

Two things this book isn't: First, if you want a book that starts from Turing's paper then delves into even more advanced mathematical research and theories, then this isn't the one for you (although it does helpfully include a summary of more recent work that follows on from Turing's ideas). Second, at the other extreme: although this book includes some biographical information, if you want a detailed non-technical biography of Turing you should look elsewhere.

But for all the rest of us between these two extremes, who want to understand what Turing machines are from the original source, then I wholeheartedly recommend this book.

My only complaint, and a very minor one, is that Petzold's description of Bletchley Park's location would place it in Suffolk rather than Buckinghamshire! But given the complexity of the book's subject matter, it is a testament to the quality of Petzold's research that this is his only error.

The book is accessible to anyone with even a basic mathematical background. At the same time it does not fudge the hard issues - it just explains them, patiently and well. There are, thank goodness, no patronizing attempts to involve knights, knaves or other fantasy figures along the way. And by the way, a big cheer for a book which finally gives the credit due to Turing as the true intellectual father of the modern programmable computer. The book makes clear the debt that Von Neumann, the supposed inventor of computer architecture, owed to Turing; Von Neumann himself, incidentally, was well aware of this, and always gave due deference to Turing as the originator of the ideas that he so ably put into practice.

One of the ironies of history is that, as the book makes clear, Turing made his astonishing landmark discovery (of the basic architecture of the general purpose computer) not because he was interested in computers, but simply as a means to the solution of an abstruse problem in mathematical logic. Seldom can the ultimate value of pure intellectual research have been so starkly illustrated.

Charles Petzold is an extremely talented author and I hope to have the time to read through his other books, He unlike other authors I have read takes the time to explain each piece of the puzzle before showing you how it comes together. Many would have heard of the name Allan Turning if you have some background in computing, but it wasn't until I read this book that I really understood what it was he did. I also found myself engrossed in Petzold's writing as he unravels turnings life and walks you through his near psychic envisioning of computers. The fact that today's computers share so many uncanny similarities to turnings idea of how they would work only shows how influential his paper was. Another point I might add is that Petzold has clearly taken great care in his work as I cant remember spotting a single typo as I read through this book, and would suggest that any readers of this book take the same care in reading it, as without his commentary I don't think I could have followed much of Turning's paper. Turning makes a few errors in his paper and Petzold explains he later publishes corrections and in some cases Petzold describes how it could have been done. I imagine many would ask them self's in the early years of studying computing today as I have, "how was it first conceived". Well this is the answer.