When I began thinking about distributed computing more seriously for my Msc work I looked at it as being an old idea. Almost as old as computers itself.. I thought. Boy, was I wrong..
Distributed computing is known to have began around 1970 with the emergence of PCs and computer networks (mainly ethernet and the Internet). As PCs were slower than the mainframes the way to scale was to buy more of them. Also, the trend toward cheaper machines made the idea of having many PCs a feasible replacement for a single mainframe. We can think of it was the parallel machine of the poor..
Although there is some controversy about what is considered to be the first computer, the difference between it and the appearance of distributed computing will always be significant. I choosed to consider the first computer the first fully programmable mechanical device by Charles Babbage that goes back to 1837. In this case, that makes a difference of 133 years, which in human history is not much but in terms of computers is a lifetime.