Although introduced with mainframe machines, the mini-computer epoch saw a complete migration of the human to computer interface away from punched cards and toward text and modest graphic mechanisms. These were first introduced through teletype terminals, which formed the earliest variants of non-voice, network communications. These terminals became the primary source of input to and then output from mini-computers. Rapid advances in the technology migrated from the mechanical teletype terminals to cathode ray tube devices that used typewriter qwerty keyboards for input and electron display tubes for output. The end result of this was a much tighter linkage between the human and the computer. Developing computer software and using the resultant software products became much more of an interactive activity.

Integrated Circuits as Genetic Selection

In 1958, Jack Kilby with Texas Instruments constructed the first integrated circuit. This device allowed for the construction and interconnection of many transistors and other semi-conductor devices on a single substrate of material. This provided yet another order of magnitude decrease in both physical size as well as electrical power consumption in order to achieve comparable computer operations. Smaller size again meant faster operation. While incredibly profound, we tend to characterize this development as comparable to genetic selection as opposed to mutation. In fact, the goal of the research and development work from which this event resulted was generally aimed toward this end.

Prior to this selection event, electrical circuits were comprised of discrete components: transistors of various sorts along with resistors, capacitors and induction coils connected by highly conducting material such as copper or gold wire. The connections between components and their conducting links were generally effected by soldering the materials together. A significant innovation that occurred across the boundary between mainframe computers and minicomputers was the wire-wrap connection. This form of interconnection involved attaching components to a mounting board that had, on its reverse side, short peg-like extensions at the connection points of the components. Then a very flexible conducting wire could be wrapped around one of these extensions for a connection point of a component and then extended to and wrapped around a different extension for a connection point of a different component. This approach had the benefit of not requiring the use of high temperature tools around potentially sensitive components.

Personal Computers

The third epoch of computers is comprised of personal computers, whose history is different from that of mainframes and mini-computers, although the trend is similar. Personal computers showed up in volume in the 1980’s, to become prevalent as mini-computer replacements in the 1990’s, until they started to also replace mainframes in some functions in the 2000’s. Personal computers sold in the hundreds of millions, a hundred times more than mini-computers, in prices around a thousand dollars, a hundred times less than mini-computers.

Personal computers brought a new type of applications into being. The best example was VisiCalc, the first spreadsheet of widespread use. A personal application, VisiCalc by itself would be enough to justify the purchase of a computer. Over time, personal computers would end up being used not only by individuals, but also in the back office as powerful servers doing tasks previously performed by mainframe or mini-computers. Coincident with the development of the

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