The title of this book is a wonderful double entendre. On the surface, the title is just a reference to the famous early computer made by Charles Babbage. However, underneath that surface reference there is another association. The computer is the Difference Engine in another sense; it is the catalyst, or the engine, behind serious changes in the culture and society that make differences appear in a very rapid way. The relocation of these changes backward in time has the effect of objectivity.
That means that as the reader sees how the computer might have affected history if invented earlier in time, they will also see the author's speculation about the objective effects of the computer. In other words, the science fiction element of the novel merely relocates the real historical impact of the computer in an earlier era to "weigh" or assess the Difference between life before the computer and life after the computer.
And what is the general effect of the computer as the authors see it? Well, right away, the novel addresses the government. With the radical changes in the economy that the computer technology implies, the status quo becomes nearly irrelevant. The old power structures are dismantled and adjusted so that the real power quickly falls into the hands of whoever understands the technology best. This is basically a commentary on modern economics, because those with mastery at computer technologies are very likely to become powerful economically.
