Why Some Old Computers are Interesting
Surely there is nothing more useless than an old computer? Progress is so swift that a newly bought machine is out of date by the time it is delivered, a two year old machine is obsolete and after five years a computer has no residual value...
Well ... yes and no. It is true that the capacity and performance of computing equipment has improved exponentially since (at least) the first stored program computers appeared circa 1948 (http://en.wikipedia.org/wiki/Manchester_Mark_I). The price/performance ratio has improved even more dramatically.
Just how fast the improvement has been is not easy to say. "Very fast indeed" is a fair summary, though. Since the dawn of integrated circuit technology "Moore's Law" http://en.wikipedia.org/wiki/Moore's_law) has held pretty much true - the number of transistors that can be feasibly put on a die has doubled about every two years. The "rule of thumb" version of Moore's Law - that performance doubles every 18 months, or a factor of 10 every 5 years - is rather too optimistic. Although for some specific microprocessor families over a relatively short time span, even the "rule of thumb" version has been true.
However, while today's microprocessors are miracles of engineering, available at an almost ridiculously low price, the greater part of the performance increase is attributable to semiconductor process technology. It is not due to architectural innovations.
