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on 19 September 2009
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.
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on 26 March 2013
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.
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on 29 May 2016
Whilst I have more than a little sympathy with DocBrown's review of this book, I suspect that the reader's background will have a great deal of impact on how Petzold's work is received and understood.

As a software developer with nearly 40 years experience I found it necessary to re-read large sections of this book, over a protracted period of time, in order for the pieces to start to fall in to place. But this I found to be an ultimately rewarding experience.

So, this is not a work to be embarked upon lightly as we are trying to pull apart and understand one of the greatest minds of the 20th century here. That taken as a given, Petzold does do a remarkable job of teasing the meaning from the intricate paragraphs of Turing's paper.

If you are unsure as to whether purchase is a wise step then take advantage of the 'look inside' option and if that does more to confuse than clarify then you will have your answer.
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on 29 August 2013
A popular exposition of Turing's daring paper on Computable Numbers would be a welcome addition to any interested party's library, since this paper is held as, "The foundation of modern computer science." This book, despite the authors stated desire and indeed the volume's format, fails to provide a layperson an understandable or pleasant acquaintance with any topic pertaining to computer logic or programming methodology.

In addition to the general style, the thought behind how the concepts are presented seems willfully obtuse. Persistent failure to analogize any of the concepts in Turing's work can be infuriating, but this book commits the cardinal sin of all technical writing by using repetitive sentences to explain deceptively simple ideas and frequently using imprecise language which only leads to confusion. More recent programming concepts are laced into explanations of Turing Machines without any specific reference to them or anything like them in the paper itself. Indeed explanation of these modern concepts themselves seem to have gone missing. Most bewildering of all however, the author tries to explain subroutines and later a branching algorithm (as well as other processes) without any diagram, tree or otherwise, whatsoever. I'm baffled as to how a layperson could expect to follow this.

I eventually reread my O'Reilly book on understanding computation, read a free e book from Mcquarie University on computer and programming logic, and then read Turing's paper on its own. I am consequently of the opinion that someone with all Petzold's enthusiasm and programming knowledge combined with the fascinating nature of Turing's thought experiments, would find it difficult to monotonously construct a book on the subject. I just want to reiterate, Petzold describes programming methodology WITHOUT diagrammatically describing the process in any way, only verbose sentences are used, it must be the result of some form of madness.

Quoting from the back cover, "From his use of binary numbers to his exploration of concepts that today's programmers will recognize as RISC processing, subroutines, algorithms and others, Turing foresaw the future.." If you understand any of these concepts and can use them in software creation, then this book may provide a nice exploration of Turing's work, you could however just read the original paper unabridged for free online. If you are unaware of these concepts in the quote, this book is practically worthless.
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on 10 June 2009
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.
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on 26 January 2011
This really is a great book and a must for computer science students.

In examining Turing's paper in detail Petzold (Or Turing) introduces Turing Machines in their original form which may be slightly unfamiliar to those who have been taught about them in the way in which they were reformulated in the 1950s. But the explanation is (mostly) clear and you come away understanding Turing's approach and much more besides.
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on 18 March 2015
Bought as a gift and recipient was very pleased with it.
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on 3 November 2013
I've just finished reading this book, and I enjoyed it greatly. Do I understand much more about Turing's work on the Entscheidungsproblem problem? No, not much, but that's my fault not the author. I know a bit more about the Turing Machine - and that IS fascinating. You can start to see where computing came from (I've been working on computers for over 40 years now, and have done a lot of study - I learn more from this book . Petzold writes engagingly, knowledgeably, and passionately about the work - and that was good enough for me to not only complete the book, but a) look at other books by Petzold; and b) look at Alonzo Church.
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