IBM Mainframes

Operator's console

The introduction of the IBM flagship eServer zSeries 990 in May 2003 was just the most recent addition to a long line of the company's mainframe computers spanning more than 50 years. This is their story -- or at least key parts of it.

"Mainframe" defined

The IBM Dictionary Of Computing defines "mainframe" as "a large computer, in particular one to which other computers can be connected so that they can share facilities the mainframe provides (for example, a System/370 computing system to which personal computers are attached so that they can upload and download programs and data). The term usually refers to hardware only, namely, main storage, execution circuitry and peripheral units."

Evolution of the mainframe

The first general purpose automatic digital computer built by IBM dates back to 1944. It was an electromechanical machine developed in conjunction with Harvard University and was known as the Automatic Sequence Controlled Calculator. It performed additions in one-third of a second and multiplications in six seconds.

In 1948, IBM introduced the Selective Sequence Electronic Calculator which contained 21,400 electrical relays and 12,500 vacuum tubes, enabling it to do thousands of calculations in seconds.

The Korean War sped the development of large-scale computers. In 1952, IBM announced its first fully electronic data processing system, the IBM 701 . The four years between the Selective Sequence Electronic Calculator and the 701 produced great advances in information technology. The 701 was only one-quarter the size of the SSEC and 25 times faster.

During the next few years, even faster and more versatile vacuum tube machines were developed. The IBM 650 was among the best known, with nearly 2,000 units produced. In fact, the 650 was the most popular computer of the 1950s.

Along with the improvement in vacuum tube machines came the introduction of the IBM RAMAC 305 in 1956. This system utilized a vertical stack of 50 aluminum disks coated with iron oxide. It permitted information to be magnetically coded on these revolving disks and entered and retrieved from the storage file on a completely random basis. Prior to this development, information had to be "batched" or sorted into sequence before processing. RAMAC, and developments which evolved from it, greatly increased the scope of data processing.

By the mid-1950s, transistors had begun to replace vacuum tubes in computers. In 1958, IBM announced the 7070 Data Processing System which incorporated solid-state technology offering several advantages over vacuum tube machines. Solid-state devices, such as the transistor, were generally smaller, more reliable and generated less heat than comparable vacuum tube components.

In 1959, IBM introduced two of its most important computers. These were the 1401 Data Processing System, widely used for business applications, and the 1620 Data Processing System, a small scientific and engineering computer used for such diverse applications as automatic typesetting, highway design and bridge building.

IBM 1401 Data Processing System

IBM 1401 Data Processing System

IBM 1401 Data Processing System
IBM 1401 Data Processing System

The following year saw the introduction of the large-scale 7000 series, the 1410 and Stretch (IBM 7030), the most powerful scientific computer designed up to that time.

These were the years when the range of systems greatly increased. Much smaller and much larger systems became available. The compact, low-cost 1440 Data Processing System , a machine designed for small and medium-sized business, was introduced in 1962. At the other end of the scale, IBM made available the 7094, a powerful system widely used in the aerospace industry for such jobs as simulation of rocket engines and for scientific computing in research laboratories around the world.

The usefulness of computers was greatly expanded by the introduction of IBM data transmission terminals enabling far-flung locations to communicate with a central computer to enter or retrieve information. This ability to communicate with the computer meant that information stored in the system could be automatically updated as transactions occurred and made available upon request to headquarters management as well as field personnel. IBM "Tele-processing" terminals were used, for example, by airlines to provide instant passenger reservation service, banks to update customer files, insurance companies to speed claims processing, factories to report production status and assure quality control, and retailers to speed ordering from wholesalers.

Yet, with all the advances in computer technology, programming and applications in the late-1950s and early-1960s, there were still obstacles to overcome in making maximum use of electronic data processing capabilities.

To provide an expandable system that would serve every data processing need, IBM redesigned its entire product line. The result was the new generation System/360, combining new electronic techniques with advanced computer concepts.

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