using vacuum tubes. An important characteristic that derived directly from the smaller physical size of components was the fact that transistors required significantly less power to achieve the same operations than would be the case with vacuum tubes. The net result was a capability to build computers that were orders of magnitude smaller in size and required proportionally less power for their operation. In addition, because of the small size of components, they could be physically situated much closer to each other; consequently electrical signals from one component had a shorter distance to travel to another component. The end result was that operations could be performed faster with transistor-based components versus vacuum tube based components.

As a corollary to components using less power, the same semiconductor based components operated at much lower temperatures compared to vacuum tubes. Thus, the computer itself dissipated much less heat when built with transistors. This had the added benefit of decreasing the requirement for air conditioning systems to keep the computer in a temperature range that was safe for all the components as well as for the human operators of the machines.

In essence, the semiconductor mutation brought with it a whole series of characteristics that both allowed the computer to perform better and to operate within the bounds of an entirely different environment compared to vacuum tube systems. The mainframe epoch of computers began with vacuum tube based systems. However, the advent of transistor based circuitry rose to the fore during expansion of mainframe technology. Thus, over the course of the epoch, we see the size of individual computers compressed from the size of large rooms to the size of closets. We see power dissipation decline from a level that required chilled water circulated through the computer circuitry in order to extract the large amounts of heat generated to a level that could be handled by chilled air based systems.

Minicomputers

The second epoch of computers arrived with the introduction of mini-computers, of which the Digital Equipment Corporation VAX series is most famous. This started with the development of small, real-time oriented computers, culminating with the PDP 16 bit series which showed up first in consistent volumes in the 1970’s. The more powerful VAX 32 bit computers replaced the PDP machines and developed in volume in the 1980’s, actually replacing mainframes in many functions. They also extended the range of computer applications thanks to their reduced costs. Mini-computers deployed in millions (a hundred times more than mainframes) and were priced in the hundreds of thousands of dollars (a hundred times less than mainframes).

Mini-computers brought new advances in the area of real-time operations. Multiple tasks could be executed concurrently serving connected devices to acquire data from them, and control them accordingly in the laboratory as well as in the field. Also, mini-computers started the era of wide-scale networks, with Digital Equipment leading the charge in creating the first homogeneous networks based on its own standard called DECnet.

Mini-computers were used intensively for scientific and technical purposes. Digital Equipment started as a small company that emerged during the time of mini-computer developments as the undisputed leader of a pack of companies whose names included Data General, Gould, Harris, Perkin-Elmer and Prime Computers. When mini-computers started to be used also for business, IBM, seeing the threat to its business, reacted by developing its own line of mini-computers (the AS/400), which proved enough to keep its customers from bolting.

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