The Mainframe and Mini Computers

In 1948, IBM decided not to manufacture computers commercially, believing, based on market research, that expense and size were prohibitive factors. Howard Aiken, who had joined IBM, remarked in 1950 that he could not ever see the need for more than six computers in the world. However, other scientists who had built prototype computers thought otherwise and assisted in the development of commercial models. The Manchester University team collaborated with the Manchester-based electrical engineering and electronics company, Ferranti, to create the first commercial computer, the Ferranti Mark I, launched in 1951. Eckert and Mauchly set up in commercial partnership in 1947, but sold their business to Remington Rand three years later. They developed the first commercial American computer, UNIVAC, for Remington Rand in 1951. The original UNIVAC model, supplied to the U.S. Bureau of Census, was the first computer to use magnetic tape for storage. More unusually, the Cambridge University team entered into collaboration with the catering company J. Lyons, which operated a chain of tea shops, to develop the LEO (Lyons Electronic Office) computer for processing business data.

IBM soon reassessed its position and in 1952 Aiken designed its first commercial computer, also its first electronic computer, the model 701. IBM soon acquired a reputation for innovation in computing and overtook Remington Rand’s early lead in the U.S. computer market. It recognized that the high power consumption (up to 100 kilowatts) and heat output of valve computers were disadvantageous, causing valves to burn out too frequently and creating uncomfortable working conditions. The alternative to the valve was the smaller and more resilient solid-state transistor, invented in December 1947 by John Bardeen, Walter Brattain, and William Shockley at Bell Laboratories of AT&T. At first, commercial transistor production had a high failure rate, so transistors were expensive. As an intermediate measure, IBM began to manufacture hybrid computers incorporating valves and transistors, which brought some gains in size and power reduction. The experimental hybrid model 604 computer, built in 1954, led to the commercial model 608 computer of 1957. IBM contracted Texas Instruments, a company that began as a manufacturer of geophysical instruments in the 1930s and moved into the semiconductor industry in the 1950s, as its transistor supplier. Two years later, the IBM model 7090 computer was fully transistorized. Reductions in size were not only beneficial to customers in terms of space savings, but also increased the speed of data processing because the electric impulses had less distance to travel.

Computer storage capacity also improved during the 1950s. In 1953, Jay Forrester of the Massachusetts Institute of Technology installed the first magnetic core memory in the Whirlwind computer, which had been developed specifically for the U.S. Navy in the 1940s. IBM’s contract to develop a successor to the Whirlwind, the SAGE computer of 1956, provided the opportunity to work on magnetic core memory and magnetic drum storage. The magnetic drum evolved into the magnetic disk. In 1957, IBM’s 305 Random Access Method of Accounting and Control (RAMAC) was the world’s first commercial computer disk storage system. In the 1950s, there was no concept of generic software, as each computer was programmed to perform the specific tasks required by the individual client. The programming process was simplified by the development of high-level computer languages that were designed for particular programming purposes. The high-level languages were supported by interpreter or compiler programs, which translated the language into binary machine code. The first of these languages, introduced by IBM, in 1956 was FORTRAN (FORmula TRANslation), which was intended for scientific and mathematical programs. For business applications, COBOL (COmmon Business Oriented Language) was introduced in 1959.

These large computers running specialized programs became known as mainframe computers. IBM had sold 1,800 mainframe computers by 1960 and 12,000 by 1964. IBM’s sales philosophy placed great emphasis on a continuing close relationship with customers. However, by the early 1960s, it became clear that smaller customers might favor a more generic approach. In 1963, the American company Digital Equipment Corporation (DEC) introduced the PDP-8, the world’s first minicomputer. The launch of the more generalist minicomputer was closely followed by the development of the first general-purpose computer language, BASIC (Beginner’s All-purpose Symbolic Instruction Code), in 1964. BASIC was written by John Kemeny and Thomas Kurtz at Dartmouth College. IBM did not immediately embrace the change in business strategy that the minicomputer represented, as it had too much invested in its mainframe strategy. However, it did respond by developing a more flexible type of mainframe architecture. In 1964, IBM launched the System/360 computer, which was conceived of as a “family” of mainframe equipment. System/360 was modular rather than highly tailored and offered a choice of processors, peripherals, and complementary software packages, allowing upgrading or expansion over time. It was a commercial success and total sales of IBM computers rose to 35,000 by 1970.

The long-term future of the mainframe was threatened by developments that made it possible to link up, or network, separate computers. AT&T’s core business gave it a vested interest in computer systems that were interoperable and accommodated multiple users, such as individual telephone exchanges. In 1969, Bell Laboratories developed the UNIX operating system, which became widely used for networking computers. Bell researchers developed a high-level, general-purpose computer language, C, which made UNIX compatible with virtually any of the existing minicomputers. When C became too restrictive for more demanding computer applications, it was modified by a Bell Laboratories researcher, Bjarne Stroustrup, to become C⁺⁺, introduced in 1983. C⁺⁺ incorporates object-oriented programming, a more flexible way of modeling data relationships and has become one of the most widely used programming languages.